Video Link :

So basically, I was just speedrunning for fun for the day and all of a sudden, in this run, I noticed that there was no zombies spawning at the start of the round. I don't know whether I did something for this to occur or what but if I somehow am able to replicate this, it might help the speedrun community for the game.

I apologise there was no audio, for some reason the audio got corrupted or smth.

I know this was 3 years ago and responding seems pointless but I'm gonna do it anyway cause why not. It may be related to something you might have done before you loaded up the game, maybe a sequence of buttons you pressed before you started the run. It could also just simply be a one-off glitch that can't be replicated consistently, which is the more likely option here.