the same happend to me on 2 different docker-containers
I have my Nextcloud installed on a VM running on my own server at home and it happened to me after upgrading Core Rule Set WAF rules. The solution that worked for me is here: Rule #920350 Host header is a numeric IP address · Issue #3673 · coreruleset/coreruleset · GitHub
If yours Nextcloud instance is running on hosting, most likely it is running behind reverse proxy with WAF enabled causing it.
Exactly the same thing. Is that a known issue in the RC?
Just updated from 30.0.10 to 31.0.4 and got to see the same error. Under 30.0.10 everything was fine. Nothing has changed (other than the update).
My config contains localhost, local ip and public domain as trusted domains.
I am also seeing another error (for the first time): Your server is not properly set up to resolve .well-known. Not sure whether this might be related.
Has anybody resolved this yet (who encountered this error after upgrading from NC 30 to NC 31 like me)? My calendar syncing and uploads from my mobile aren’t working anymore. 
BTW: I also have one older version of NC running with the exact same reverse proxy config and it is not complaining about not being configured correctly.
So, was there a breaking change in NC 31?
didnt work
it is a autoscaling linux not fedora
nope i tried this but still no luck