How to get consistent manger spawn on directed mode?

[Bobr]

The strat of going to round 11 and staying there doesn't work anymore. Its always a vermin round and then the mangler only spawns like 1/3 times after that. Quitting and saving to reload also doesn't work. I've tried it dozens of times.

Are there any other rounds that have a higher chance of spawning manglers? or a different map? Or do I do something in a different order to get better mangler spawns?