One suggestion – make sure that the permalink that you are navigating to is exactly the one you want. If you have trashed a ‘first version’ of the About page and started over using the same page title the permalink will not be ‘about’ it will be something like ‘about-2’
Placing the first version in the trash folder does not delete it, it just makes it inaccessible. You can always restore it if you want. It does not get removed from the database until you ’empty trash.’ Since it is still in the database, WordPress needs some way to differentiate between the two pages – so it adds a number to the second version of a page with a title identical to one already in the database.
The page/post ID is unique, so using that type permalink would work, but if you are using the page/post name then the trashed version will return a 404.
I hope the problem is this simple.