Upgrading to NC31 has been nothing but a nightmare of issues!
I am having CSRF issues that are essentially breaking up everything from simple access to files, through problems with even logging in!
I have found some issues open on GH already about these problems.
i.e. this [Bug]: Invalid response 401 in Files app - not fixed · Issue #50982 · nextcloud/server · GitHub
Sorry I moved this. The linked report is about NC 30, so it is not a specific update/upgrade issue for NC 31.
With some luck issues from NC30 can be fixed in NC 31, but there is also a high chance that they persist.
It is still an issue under NC31… Actually, I never had that issue on NC30, but as soon as I’ve upgraded to NC31 I started having it. But OK… Thanks anyway 
In this case, it might be something else (however same/similar symptoms).
In such a case, it is perhaps a good idea to open a new bug report on github.
Interesting… I’ve disabled the Redis container and configuration and the issues are all gone!
Maybe something was cached from before the update? I have also seen this on the browser side that you had to reload and/or clean the cache.
If you enable it again, does it still create this problem?