I installed the Matrix Synapse Server using the chapter in the official NixOS manual (NixOS 23.11 manual | Nix & NixOS).
It generally works, however I do not seem to be able to connect to other matrix homeservers, I cannot open a conversation in both directions.
Has anybody experienced similar problems?
At some point over the last few months my riot client can’t connect if I’m on my home network which hosts my matrix server. I’m almost always on my work vpn these days, though, so I’ve spent zero time researching. 
are we talking about element or riot (on which NixOS btw?) and do you use the web-client or the desktop client?
Just checked my element-web@1.7.5 that appears to work fine.
I’m using riot on NixOS 20.03 and element on my Android phone. Both have the same strange issue of disconnecting whenever on the same network as my synapse server.
In case my explanation above was unclear, my issue is very different.
I can connect to my homeserver using the element client, but I can’t join any rooms or open chats with users on other homeservers.