Tell us what you are trying to do?
1. Updated the broken page
2. deactivated other plugins
Is there any documentation that you are following?
Is there a similar example that we can see?
1. Open the page in hebrew (defined as default language) hidden link
2. --> Change language --> english (or russian) --> error 404
3. Open the broken page from wp-admin --> Go to edit --> the page is exist with it correct content --> try open the "View" page link --> error 404
4. In the "Edit" page mode --> Change the page permalink --> Update ---> Open "View permalink" -> Error 404
What is the link to your site? hidden link
PS. Now I disabled the english because the all page (inside the main page) is broken