The 12 Biggest CMS Migration Mistakes (And How I've Seen Each One Destroy Websites)

I've overseen probably 50+ CMS migrations in my career. Some went smoothly. Most had hiccups. A few were absolute disasters that still keep me up at night.

The worst one? A site that lost 80% of its organic traffic overnight. The client called me in a panic. "Google is gone," she said. "Everything's just... gone."

Turns out, their developer had migrated their blog from WordPress to a custom platform and forgotten to set up redirects. Fifteen thousand blog posts, years of SEO work, just... poof. Dead links everywhere.

We fixed it. Eventually. But it took three months to recover even half the traffic. The company lost roughly $200,000 in that time.

That's the kind of mistake I'm talking about. Let me walk you through the migration disasters I've seen so you can avoid them.

Mistake #1: Not Having a Backup (The Cardinal Sin)

This should be obvious, but I've seen it happen.

A developer starts migrating a site. Something goes wrong. They try to roll back. The backup is corrupted. Or worse, there is no backup.

Real story: A client's developer was migrating them from Joomla to WordPress. Halfway through, the server crashed. No backup. The site was just... gone.

They had to rebuild everything from scratch. Thousands of pages. All the content had to be rewritten from memory and cached versions. It took four months.

The Rule: Before ANYTHING happens, create multiple backups:
- Full database backup
- All files backed up
- Store backups in multiple locations
- Test that you can actually restore from the backups

I use the 3-2-1 rule: 3 copies of data, on 2 different media, with 1 off-site.

Mistake #2: No Redirect Map

This is the one that destroyed that client's Google traffic I mentioned.

When you migrate to a new CMS, URLs often change. Maybe you're going from:

old-site.com/index.php?id=123

new-site.com/blog/article-title

If you don't set up 301 redirects from old URLs to new URLs, you'll lose:
- All your SEO rankings
- All incoming links
- All bookmarked pages
- All Google indexed pages

Real story: An e-commerce site migrated from Magento to Shopify. They didn't redirect product pages properly. Result: 60% drop in organic traffic and sales tanked for three months.

The Fix:
1. Export all old URLs
2. Map them to new URLs
3. Set up 301 redirects
4. Test every. Single. One.

I use a spreadsheet with columns:
- Old URL
- New URL
- Status Code
- Notes

Then I write a script to test each redirect and make sure it works.

Mistake #3: Migrating During Peak Season

A client once insisted on migrating their e-commerce site in November. I said, "That's Black Friday month. Are you insane?"

They insisted anyway.

The migration had issues. The site was partially broken during their busiest week of the year. They lost an estimated $150,000 in sales.

The Rule: Migrate during your slowest period. For most businesses:
- Retail/E-commerce: January-February (after holidays)
- B2B: July-August (summer lull)
- B2C Services: Depends on your business

Never, ever migrate during:
- Holiday seasons
- Major sales events
- Product launches
- Peak traffic periods

Real story: I migrated a educational site in July (summer break for them). Any issues? We had time to fix them before students returned in September. Smart timing.

Mistake #4: Not Testing Enough

"It works on my computer" is not good enough.

I've seen developers migrate sites and test only:
- The homepage
- One blog post
- Maybe a product page

Then go live. And discover:
- Contact forms don't work
- Cart checkout breaks
- Search is broken
- Images aren't loading
- Mobile is a mess

Real story: A site migrated from WordPress to Drupal. Looked great. Went live. Nobody could submit the contact form. The lead generation dried up instantly. Took two days to notice and fix. Cost in lost leads: hard to quantify, but definitely thousands.

The Testing Checklist:
- [ ] Every page template
- [ ] All forms (submit actual test data)
- [ ] Shopping cart and checkout
- [ ] User registration/login
- [ ] Search functionality
- [ ] Mobile responsiveness
- [ ] All integrations (email, CRM, analytics)
- [ ] Speed test (page load times)
- [ ] Cross-browser testing
- [ ] 404 error page
- [ ] Security (SSL, forms, user data)

I usually spend a full day just clicking around and testing everything I can think of.

Mistake #5: Forgetting About Email

Many sites have email tied to their domain:
- Contact forms
- Transactional emails
- Newsletters
- Account notifications

Migrate carelessly, and these break.

Real story: An e-commerce site migrated to Shopify. Order confirmation emails stopped sending. Customers weren't getting receipts. Support tickets exploded. They didn't notice for three days because... nobody was monitoring.

The Fix:
- Document all email functions
- Test each one after migration
- Monitor email deliverability for weeks after

I keep a list:
- Contact form submissions
- Order confirmations
- Password resets
- Welcome emails
- Shipping notifications
- Etc.

Test them all.

Mistake #6: Ignoring SEO Settings

URLs are just one part. There's also:
- Meta titles and descriptions
- Alt text on images
- XML sitemap
- Robots.txt
- Canonical URLs
- Schema markup
- Open Graph tags

Real story: Site migrated to a new CMS. Forgot to set up the XML sitemap. Google couldn't find new content. Indexing basically stopped. Took three weeks to notice. By then, they'd published 30 blog posts that Google didn't know existed.

The SEO Checklist:
- [ ] All meta titles migrated
- [ ] All meta descriptions migrated
- [ ] Image alt text preserved
- [ ] XML sitemap generated and submitted
- [ ] Robots.txt configured correctly
- [ ] Google Search Console verified
- [ ] Google Analytics working
- [ ] Canonical tags set up
- [ ] Structured data/schema in place
- [ ] 404 page custom designed

Before and after migration, I run SEO audits using tools like Screaming Frog to catch any issues.

Mistake #7: Not Planning for Downtime

Some migrations can be done with zero downtime. Most have at least a few minutes.

But I've seen developers take sites offline for:
- "Just an hour" that became six hours
- "Over the weekend" that bled into Monday
- "Quick update" that broke everything

Real story: Developer started a migration Friday evening. "Just a few hours," he said. Something went wrong. Site was down all weekend. It was a restaurant's site. They lost weekend reservations. Owner was furious.

The Rule:
- Schedule downtime during lowest traffic period
- Put up a professional "under maintenance" page
- Communicate in advance (email, social media)
- Have a rollback plan if things go wrong
- Set a hard deadline (if not done by X, rollback)

I always set up a maintenance page with:
- When we'll be back
- Why we're doing this
- Contact information for urgent issues
- Social media links

Mistake #8: Losing Content

This sounds ridiculous, but it happens.

Images don't migrate. Blog posts get corrupted. Comments disappear. Videos break.

Real story: Site migrated from Drupal to WordPress. Somewhere in the process, six months of blog comments were lost. Valuable user discussions, feedback, questions – gone. Couldn't recover them.

The Protection:
- Content audit before migration (count everything)
- Verify everything after migration
- Compare databases
- Check media library thoroughly
- Test random samples of content

I literally count:
- Total pages
- Total blog posts
- Total images
- Total products (if e-commerce)
- Total users

Before and after. Numbers must match.

Mistake #9: Migrating Plugins/Extensions Blindly

WordPress plugin ≠ Drupal module ≠ Shopify app

When you migrate platforms, plugins don't come with you. You need to:
- List all functionality
- Find equivalent features in new platform
- Set up and configure everything fresh
- Test thoroughly

Real story: Site migrated from WordPress to Webflow. They had 20 WordPress plugins. Half the functionality just... disappeared after migration. Nobody had made a list. Nobody knew what features they were losing until they were gone.

Some features they couldn't replicate in Webflow. Had to add third-party tools, increasing monthly costs.

The Plugin Audit:
Before migration, make a spreadsheet:
- Plugin name
- What it does
- Critical or nice-to-have
- Equivalent in new platform
- Configuration settings

Mistake #10: Underestimating Timeline and Cost

Developer says: "Two weeks, $2,000."

Reality: Six weeks, $8,000.

This happens ALL THE TIME.

Real story: Client was quoted two weeks for a migration. Developer discovered the old CMS had a weird database structure. Custom code was required. Timeline became two months. Budget doubled. Client was not happy.

The Reality:
Migrations always take longer than estimated. Always.

My Rule of Thumb:
- Developer estimates 2 weeks → Plan for 4 weeks
- Developer quotes $5,000 → Budget for $7,500
- Any unforeseen issues → Add another week

Better to be pleasantly surprised than scrambling for more money and time.

Mistake #11: Not Training Staff

You migrate to a new CMS. Your team doesn't know how to use it.

Content updates stop. Nobody can add blog posts. Product listings get stale.

Real story: Company migrated from WordPress to Drupal. Their marketing team (non-technical) was comfortable with WordPress. Drupal's interface confused them. Content publishing ground to a halt. They eventually had to hire Drupal specialists, adding unexpected costs.

The Fix:
- Train all staff before launch
- Create documentation (how to add a blog post, how to update pages)
- Record video tutorials
- Have developer on standby for first few weeks
- Consider complexity in platform choice

If your team struggles with WordPress, don't migrate to Drupal. Choose something easier.

Mistake #12: No Post-Migration Monitoring

Migration successful. Site is live. Everyone celebrates.

Two weeks later: traffic is down 30%. Nobody noticed until client checked analytics.

Real story: Site migrated, everything looked good. Three weeks later, they realized search functionality was broken. Users couldn't find products. Bounce rate had spiked. Sales were down. The break happened during migration but nobody was monitoring.

The Monitoring Plan:

Week 1 after migration:
- Check analytics daily
- Monitor error logs
- Test all forms/functions
- Watch for user complaints
- Track conversion rates

Week 2-4:
- Check analytics every few days
- Monitor search console for errors
- Review server performance
- Check for broken links

Month 2-3:
- Weekly check-ins
- Verify SEO rankings recovering
- Monitor site speed
- User experience feedback

I use tools like:
- Google Analytics (traffic patterns)
- Google Search Console (indexing, errors)
- Uptime monitors (site availability)
- Speed testing tools
- Heat mapping (user behavior)

The Perfect Migration Checklist

Based on all these mistakes, here's the checklist I actually use:

2-4 Weeks Before:
- [ ] Full audit of current site
- [ ] Content inventory
- [ ] Plugin/functionality list
- [ ] SEO audit
- [ ] Create multiple backups
- [ ] Choose migration timing
- [ ] Build redirect map
- [ ] Set up staging environment

1 Week Before:
- [ ] Final backups
- [ ] Test staging site thoroughly
- [ ] Prepare maintenance page
- [ ] Notify users of downtime
- [ ] Brief staff on new system
- [ ] Prepare rollback plan

Migration Day:
- [ ] Put up maintenance page
- [ ] Migrate content
- [ ] Set up redirects
- [ ] Configure new CMS
- [ ] Test everything
- [ ] Go live OR rollback

Post-Migration:
- [ ] Remove maintenance page
- [ ] Test all functions again (live)
- [ ] Submit new sitemap
- [ ] Monitor analytics
- [ ] Check error logs
- [ ] Verify email functions
- [ ] Test user accounts
- [ ] Speed test
- [ ] Mobile test
- [ ] Monitor for 30 days

30 Days Later:
- [ ] SEO performance review
- [ ] Traffic comparison
- [ ] User feedback collected
- [ ] Final testing
- [ ] Document any issues and fixes

When NOT to Migrate

Sometimes, migration is the wrong choice. Consider NOT migrating if:

Your current platform works fine
Don't fix what isn't broken. "Newer" doesn't always mean "better."

You can't afford downtime
Some businesses literally cannot go offline. Even an hour costs thousands.

Your team isn't ready
If staff can't handle the new platform, you'll have ongoing problems.

Budget is too tight
Migrations cost more than you think. Don't start what you can't finish.

You're doing it for wrong reasons
"Everyone uses Platform X" is not a reason. "We need specific features only Platform X offers" is.

The Bottom Line

CMS migrations are risky. They can:
- Destroy your SEO
- Break functionality
- Lose data
- Cost way more than planned
- Take much longer than expected

But they're sometimes necessary. Technology evolves. Business needs change. Platforms become outdated.

If you must migrate:
- Plan thoroughly
- Back up everything
- Test exhaustively
- Monitor constantly
- Budget 1.5x time and money
- Have a rollback plan

I've seen migrations go smoothly. It's beautiful when it works. Clean, fast, no issues, SEO intact, everything better.

But I've also seen the disasters. And trust me, you don't want to be that person calling me in a panic because your site is down, your traffic is gone, and you have no idea how to fix it.

Learn from others' mistakes. Don't repeat them.

Now if you'll excuse me, I have a migration next week to plan. I'll be following this checklist because I'm not stupid enough to think I'm above making these mistakes myself.

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Planning a migration? Show me your checklist in the comments. I'll tell you what you're forgetting.