Error 520 when accessing page but goes away after refreshing a few times

When accessing my websites protected by Cloudflare, there randomly appears an Error 520. After a few refreshes, everything works again for the next few minutes until the error starts popping up again, and so on…
This is basically a visualized construction of my current infrastructure (drew that last night, so don’t expect too much):

(C1, C2, … basically means Docker containers)
“Proxy” in this case is another host which’ll proxy all request to the host on the left.
Also: when this error occurs, there’s nothing in the log (neither on both hosts), maybe I looked in the wrong logs?

Does somebody know how to fix this issue? I already tried toggling switches (HTTP/2 & 3, etc.) in the Cloudflare dashboard.
If you need any resources to help me, go ahead and ask!

It seems like my hoster put on another DDoS protection configuration for the Proxy VPS than for the main server :slight_smile: “syncing” that config resolved the issue.