how

Its random, you basically just have to keep restarting until you get lucky but it does happen.

if someone see this in the future, i'm going to explain

basically you need to enter and leave swampfire easy level until the spawners don't work, then you beat the level and now every spawner in any level don't work

i'm not sure if you need to do this in swampfire easy level or if you need to beat it, but this always works for me