I have this happen fairly often too. something like once out of every three games or so.
It’s always the same: New round, I instantly drag the window off to the right. It seems as though it’s when I move it quickly, not sure, but get it far enough that part of it is off the screen, and it goes poof.
It really sucked the other night when I went through a whole game without buying anything, then planned to go on a spending spree (and likely win) in the last round. lol