I probably clicked 'Cancel' on Multiplayer screen and at the same time game accepted automatically itself and paired with another player. As a result, I had a menu overlapping the gamplay. This part of screen was complitely non-clickable, I could only build 2 units and I haven't seen my commander anymore (btw. is there a way to build a unit from the keyboard shortcut?)
There should be at least some bonus for playing like that ;)
Pictures attached.
Cheers,
Paweł