I had a little problem at start from a trip.
During Check-In, one passenger request a ticket, and when I went to sale, I've got stucked, no ESC key, or any command worked anymore and I needed to force game to quit.
I recorded this video to show:
Ticket Sale session in Flixbus App also have no working controls, and icons to reject or accept disappeared too.
I couldn't walk, or hold Smartphone.
My guess: This happened when I tried to acess Settings menu, during ticket processing to passenger.