Do you use collection factories? or normal factories that create GOs? Documentation states that collisions don’t work between collision objects in different collections.
it’s not super interesting from a programming point of view, but you can play here if you want:
I made this a few years ago (damn, i am getting old, and weirdly obsessed with this game mechanic…) and I’m remaking it now that i know a lot more about Lua and how it all works.