I was working with the mob_spawns, and I found that any invasion that needed an invasion count higher than 3 will not spawn. I had used the technique used here:
https://coros.us/wiki/index.php?title=Hostile_Worlds_-_Invasions_-_Customizing\
to cause an invasion to spawn and end several times, but It would never give me any invasion that required an invasion_count beyond 3. I did make sure my json was correct.

So far this is an excellent mod, sorry if this isn't the best issue tracker.