I use this app called Couch Potato to control my Xubuntu laptop plugged to the TV through HDMI using my Android smartphone (I can control the cursor and send keyboard input through it). On the laptop I open this Java app ("java -jar Server.jar", nothing interesting, see screenshot). With the Android on the same LAN I open the app, it will find my laptop IP running the server, then I can simply connect to it.
For some months it worked wonderfully, but now after some hours using it the IP stops showing up on the Android app. I have to reboot (or log off) my laptop and open the Java program for it to work again. This makes me think it's some power or wi-fi setting on the Xubuntu end kicking in, but I can pinpoint what it is.
I'm not looking for a solution to the Couch Potato problem (although this would be cool too). I want to understand what Linux mechanism started doing this out of nowhere. From what I can recall I haven't made any relevant change to my install.