Random game over upon quiting game

I started a new game in an attempt to test some new maps. After a while of nothing new, I desided I was done. Before I exited out, an interception popped up. I sent planes to intercept, then I quit the game. When I got to the main menu, the losing game over popped up. I never saved in any of this, as the save was not important to me

Known bug afaik.

It's a known issue