We get called in to fix these more often than we get called in to prevent them. The causes are remarkably consistent.
1. No redirect map
Every old URL needs a destination decided deliberately. Bulk-redirecting everything to the homepage tells search engines the old content is gone.
2. Changing URLs without reason
If a URL ranks, keep it. Tidier slugs are not worth the risk.
3. Losing internal links
A rebuild often drops the contextual links between pages, and with them the internal authority that made key pages rank.
4. Not checking the logs
Analytics tells you about people. Log files tell you what search engines actually crawled. After a migration, only the second one answers the question you need answered.
- SEO
- Migration