Sorry for the late reply, still having the issue, on three different PCs, also friends having shared libraries the same issue. It is like I said it is.
It seems to work until a random time, mostly when the server changes IPs, then the clients, just the Windows 8/10 app, doesnt work anymore, shows the shared server as offline. When I go to settings logout, and login again, it finds the server, and works.
Clicking refresh doesnt work. I need to logout, login (in the app), then it finds the server.
App version is 2.1.0.6, it worked before for over 1,5 years, but since going to Windows 10 it doesnt anymore, it since one of the last app updates, cant say which triggered it.
It is a shared library btw to a internet shared server, not a local server.
Server is also newest version, linux.
Just tested it again, opened the plex app on my laptop => server offline. Went to settings logout, logged in again, aaand app found the server ( before refresh did nothing / stayed offline). Now I can watch/browse through the server.
Now opened the app on my tablet, offline… did the same procedure, server goes online / is found.
It will mostly work now for 24h, then tomorrow, broken again.
“It sounds like the client is pinging the server periodically to test availability and those tests are failing” this sounds to me you / devs, changed something in the client which broke it (on some networks / scenarios), because it always worked over the last years perfectly, and just started to be broken recently.