"There was a problem controlling the selected DLNA device. Double-check your device, server and network settings."
This means that MC was unable to send an HTTP SOAP command to your renderer. This means that either the renderer has crashed, stopped responding or gone offline.
I have not tried leaving MC in a failed state to see if it eventually recovers connectivity when something times out or the like.
The CPU thread within MC that issues such HTTP SOAP commands may freeze if it encounters such an error. Especially if MC was able to open a socket connection to the renderer and send the command (meaning the renderer is partly alive), but that MC is then left waiting for a response from the renderer (meaning the renderer is definitely not fully functional). In such case, that CPU thread will "hang", and this sometimes causes other parts of MC to also "hang".
If I may say so, I think that MC is not completely perfect when it comes to thread isolation, thread synchronisation, and killing and cleaning up dead threads. However this is very tricky stuff to program properly and to debug, so I "forgive" MC for such imperfections. I know this from my experience in writing Whitebear, which is also I admit not perfect in this respect...
Anyway, it is indeed worthwhile waiting a minute or two to see if MC does recover.
PS one reason why, when you kill and restart MC, that it may not be able to talk to the renderer, could be that the "hung" TCP socket connection between your PC and the renderer may not have been cleanly closed, and indeed the Windows IP stack may be holding open the socket to the renderer, and thus preventing anything else from opening a socket to the renderer. In other words, I suspect that the renderer is
also not perfect when it comes to thread isolation, thread synchronisation, and killing and cleaning up dead threads...