I had a problem after upgrading my cs-cart from V3 to V4 and after important my old data to the new system. SEO pages stopped to work. a 404 page disappears.
It took my a lot of time to figure out the solution.
The solution was simple
- copy “.htaccess” file from your old cs-cart to the new one
- edit “.htaccess” and add the folder of your new cs-cart to index.php path