I'm a bit far away from it to remember exactly where it was, but it was in the dark hallways where you first encounter the faster cybernetic zombies - there's a Smart Gun on the far side of the arena in a weapons locker.

There's a checkpoint that triggers right before the second wave busts down the door and floods into the area, and it worked for the first several attempts, but after that, the door wouldn't bust down.

It BLOWS that I found a softlock this late into the run...is there any way to start a campaign from a selected episode? Or do I gotta do it all over again?