I found a potential solution to spawning in the debug forest when I was spawning in there pretty much all of the time, I often alt-tabbed while waiting as it often took 10+ mins, I decided that it might be the cause so I abstained from it and low and behold it's worked so far! I'm not sure if I've just been lucky and it's a coincidence but if it frequently happens to you then you should give it a go.