I have the same issue with the game, since day one. I kind of learned to accept it but to be honest if you are in a survival map at wave 18 or higher and just want to tab out, to do whatever, it kills the fun instantly. Most of the time I try to build akf builds and the waves are pretty long so I would like to watch a YouTube video or just listen to some music, but at the current state it's simply not possible. I tried all modes full screen, border less window and window, I also tried different settings and resolutions, but the game just freezes up and the only option I have is to hard reset my pc because nothing else responses anymore for quite a long time. I would love to get this problem fixed.