In my experience with custom collisions, I have learned UE4 is a very ducking duck and it loves web feet. It takes an L and turns it into a triangle. You have to separate so much (make a complex gear see what I mean. Make three cubes miles apart again and see or even make a bloody bowl.).
It also has 3 different tags you need to remember.
My suggestion is to get rid of the 3 tags, get rid of the web footing issue and just have it go something like this.
Coll_Object_00. The program sees Coll (collision) and goes oh this is a custom collision take it literally with no interpretation. Much how you do complex collision it does it exactly as the mesh is. Not this lets web together c…ra…p that makes no sense to web together. Not this let’s make you make a thousand different parts to get exactly the collision you want. Just one tag, the program does as most software does and takes it literally. These odd tags are not even something that really makes sense to anyone just walking in at least Coll makes sense short for Collison the random letters (I am aware they stand for stuff but they seem random at first) that I probably will never remember don’t.
So yeah no more ducking, just literal this is a collision mesh, set it as a literal collision mesh or just have that as a bloody option if you do not like too much change. Tag it with Coll, upon import it goes oh, a literal collision mesh, and with the others, it still goes oh this is a web-footed one potentially lets cap off things that do not need capping, etc. Personally, I do not get the web-footed ways and vote for it to be trashed and replaced with literal collision mesh but that would break a lot of projects. If there is a valid reason for software to assume that the collision you just made is meant to be a blob instead then, by all means, let me know what is a valid reason for this atrocity.
Anyways that is my suggestion, ducks are cute in the real world but their feet are not needed for collisions.