Cache problem? failed to load resource: the server responded with a status of 522 ()

So, I have django site running with ubuntu server and set up with cloudflare.
Before, that was ok. But after sometime, it can’t choose dropdown menu and show the bug is failed to load resource: the server responded with a status of 522 (). And when I turn on development mode, then I can use it again.

I think there is some problems in caching?

I have that same problem. I could not figure it out either. I’m getting an error 522.