That helps, thanks. 
Yeah, for the most part I am using many of these meshes as part of a procedural foliage actor to scatter stones and boulders throughout my forest rather than dropping them individually.
I’ve tried almost every type of collision I can think of and no matter what, my avatar just walks through it. (although it doesn’t show on the clip, I resimulated the forest each time I saved the collision).
It’s driving me insane LOL Especially since adding collision to the trees in the same manner worked perfectly.