Error 520 (randomly) while loading cloud with CloudFlare

Hey there. From one day on the other (maybe when I updated NCP) or maybe also when I installed more docker services it happened that I get error 520 while loading pages of the cloud and I don’t get why.

I’m running NextCloudPi as Docker container with CloudFlare. I also have a HAR file if this could help.
You can see it is random. This is the settings page of nextcloud and when I reload this page I won’t get 520 errors for every icon again. I need to press Ctrl + F5 multiple times (reload) and then the page will be loaded completely and correct.

The header is not above 8MB. Just 2.7MB. I did not really change anything in my nginx configuration. I see no error logs for the cloud of nginx and also not of the NCP container.