Why this happens.
Rankings belong to specific URLs. Change those URLs without a plan and search engines lose track of your pages, and so do visitors with old links.
What not to do
[YOU]: the most expensive relaunch mistake you have seen a client make before calling you.
How I’d approach it
I map every existing URL to its new home before a single page goes live, plan redirects, content and tracking up front, and check rankings every day for the first weeks after launch.
