LMDE
Oops! I thought it was some obscure DE.
Considering your points, it seems to be most probably some configuration issue.
Might even be that some of the automated monitor/display configuration tools (might be some GUI settings thing) wonked out and reconfigured something.
If your system has some shortcut combination for selecting external monitor/connected projector/mirror screen, perhaps you can try that.
Also, since you mentioned xrandr
, I would assume X Session. You can also use xrandr
to check and set the monitor configuration. Not just whether it is connected, but also location (left/right/up/down) and screen resolution of each display separately. Perhaps trying those could tell you what is happening.
This output is just for the network firewall.
In this case, you might want to ignore all messages with this pattern.
Perhaps look into other messages