YACReader apps unable to connect to server

No fixes on my end. I think that the fact that other apps where also affected means that it was a problem in your network. Plex has its own servers that work as a gateway to connect devices, so they probably were using the right connection path because of that (or maybe it was using the streaming through their server which is also possible).

I haven't a clue, then. Well, I do, but it's a guess -- that Windows reset something, say the streaming media setup, and I set it back. Now I need to see if audiobookshelf is working again.

Plex is another kettle of fish. On one of my servers I can't create or edit libraries, so what I have is immutable until I redo Plex again.