How to track down failure of discourse upstream inside container resulting in 502 Bad Gateway

Yes, I’m using data explorer. I didn’t do a git pull before restarting.
When I do a git pull, and then ./launcher restart app it’s not fixed.

Except that I’m running it behind an nginx on the host.
(And I have a few plugins, such as data explorer.)

I’m now trying ./launcher rebuild app - I hope that rebuilding the app will preserve my forum’s database … and I’m not ending up with my forum reset.
Doing launcher rebuild app does not address the issue.

This post describes an issue with privileged vs unprivileged containers, but doesn’t provide more information. It’s also from 2 years ago so may not be related to a recent update.