Hey Eric,
The particles are just being placed in the level when the issue occurs (although it also happens if I activate them when overlapping a trigger box).
Right now they are colliding with blocking volumes and any mesh (even if they don’t have collision enabled).
Here are the screenshots you required, hope this helps 
(I assumed by behaviour module you meant Event generator and receiver modules - let me know if I’m missing anything haha)
Thanks for your help!