I upgraded one of my sites to 2.3.4 and it broke. I ended up with two home pages and several menu items missing. The extra homepage was the default SS homepage. Not liking a broken site, I blew away the database and restored it from my backup and blew away the files and restored those from backup. The end result even after numerous /dev/builds and / or ?flush=1 is a site with exactly the same problems:
1) two home pages - the SS default homepage gets re-created whenever it doesn't exist and a /dev/build is run
2) A number of pages which do exist do not appear in the menus. They exist in the backend and are set to display in the menu.
This isn't a cache problem as 5 different computers on 3 different internet connections all see the site the same way.