Slaughterhouse 3000 bosses

I completed slaughterhouse 3000 about 5 times today. Only problem is red rain and blue fire never spawning.

Does anyone know how i get those 2 or are they random?

Sometimes the flying enemies get stuck in the wall and you cannot progress until they are killed, all you can do is try restarting the wave.

Their drops are kinda fked too. They drop stuff on their platforms and when you go out there to try and pick the stuff up, you die.

Yeah but i completed all waves so that’s what i don’t understand :man_facepalming::cold_sweat: