Edit: I fixed my problem by re-making my nginx reverse proxy and a do-over of my proxy hosts. I have yet to restart my server, though ...

I'm a beginner with all of this stuff, so I'm sure I'm not assessing correctly what's wrong with my setup. It's more of a methodical "trial and error" approach, that I have, where I change one thing at a time and see what happens ... quite time consuming but it helps me to figure things out along the way :)

However, if you have an idea, what could be wrong with my server, I'd appreciate any ideas: I run Nginx Reverse Proxy with nginx in a container within a custom network "my_network" and have assigned that container a fixed IP. I run other containers (portainer, mariadb, nextcloud, synapse) that all connect to the same custom network. The nginx container "see's" the outside web with ports 80 and 443 openend on the firewall for that container's fixed ip and routes traffic (and needed other ports) to my other containers. This is all working well and also works after restarting the server.

Now I tried to install a lemmy instance and got it up and running by bringing the lemmy containers in my custom network as well and proxy'img my nginx to the lemmy proxy. However, when I made a restart of the server, something broke and I cannot get the web-ui of NPM to load. I think somehow host names and/or IP adresses got mixed up somewhere. The containers start just fine, but I can't access it with web-ui anymore. Also reverse proxy-ing doesn't work, but if I open the needed ports on my firewall manually I can access the other services containers.

I hope this is even understandable, not sure if I'm using the correct terms ..