I have an Echo dot going into the line in of my Play5 in my bedroom. I've grouped it with my living room (Playbar plus SUB) before, but it's not grouped now. I'll be listening to Sirius radio as the source in my living room, for example, and all of a sudden it just jumps to the line in source from my bedroom - totally randomly, and it happens periodically throughout the day. I'm not sure if Alexa is "waking up" for some reason and starting to play something, but it shouldn't matter; because as a result of this problem also occurring in the bedroom (play5 just starts playing randomly in the other room), I always have that on mute. I can't figure out why this is happening.
I'm going to start removing culprits, one at-a-time, like unplugging the Echo Dot and see if it keeps switching sources, and maybe even reset the controller; but this is really getting annoying.
This is pretty much a call-out, to see if anyone else has seen such funkiness.