Character Cloth: Weird interaction with 3D Software-made environment collision

So I have a very odd clothing issue with my clothing set-up. For some reason, the whole project works fine as long that I use collisions made entirely in-engine… but if I make custom collisions, say from 3DS Max or Blender, then I’ll start having massive glitches happening with the cloth:

The collision in this example has six rectangular collisions. They’re very basic.

I never saw that before and to be honest, I’m not even sure where to start to find a solution. Everything works fine as long that I keep the collisions entirely made in-engine, but that’s not practical for more complex shapes. Anyone had a similar issue?

EDIT: It seems the issue stick as long that any custom collision is within a simple mesh, regardless of the state of the collision itself. For instance, I’ve deactivated the block collision and changed it all to “ignore”. The character can run through the mesh, but the clothing itself still reacts badly. I am using UE4 4.22.3.

EDIT 2: Tried with 4.23. Same issue.

EDIT 3: For some reason, it seems like sometime, custom collisions gets merged in a single mesh when imported into UE4. I exported the collision from UE4 and noticed the issue when I imported in Blender. All the collisions - that were hand-made to be convex - were collapsed into one big mesh and I had to split them back manually. I reimported - and it seems to have fixed the issue… It’s odd, because the gameplay works flawlessly with the collision “merge” otherwise.