Found a crash- when firing either shotgun pointblank into a zombie, the game freezes and I have to restart my computer. Happened to me a few times now. I think you may need other zombies behind the targeted one to cause it. If it doesn’t freeze, then the frames will plummet for a second before resuming. On all my crashes, it froze on a frame that showed the blood spray particle effect taking up the whole screen. Maybe all those pellets trying to make a blood particle simultaneously, taking up the entire screen, is a bit too much for the program to handle? Not sure.
Also there’s some sweet spots you can jump to that the zombies can’t reach, notably the fallen shelf upstairs, two different sets of debris in the starting room, and the two shelves in the mystery box room that you can crouch-jump on-top of. My favourite spot is on-top of the left hand wall of the mystery box stairs. There's a concrete bulge in the wall that that gets cut off by the hole in the second floor wall. If you jump to the top of the bulge from the second floor, leaping over the stairs, you can land on the bulge and camp there as long as you hold down the w key. By jumping backwards, you can just hold the s key and face the zombies to shoot them.