The issue seems to be that it ignores the cache control headers, for instance: https://stackoverflow.com/questions/48693693/macos-safari-ca...
It puts the logged out version of a page in cache, then after you log in it keeps showing you that version instead of the new one.
If that’s the issue, you can solve it by clearing the cache in Safari. On iOS, go to Settings → Safari.
For the website where we had this problem, after some initial work it was working on Safari/MacOS but not on Safari/iOS. We eventually hammered the headers hard enough for Safari to acknowledge them, but lots of users were still locked out since Safari would of course not pick up the updated page, and the only solution has been for each user on iOS to clear their Safari cache.