Not in a game, but can't join queues after losing connection.

I was playing a custom game but lost connection (network hardware issue). I exited SupCom and returned to the matchmaking screen under the 'Play' tab, but it says "Can't join queues while you are in game" - the game isn't even open.

I was able to fix it by logging out of FAF and opening the client again.

I have had this too a number of times, sometimes solving it isn't trivial

Use the superior python client.