I am not sure whether this helps, but I can share some experience I made with Apex cloth (working with 4.15 batch then):
First, I once had this problem as well and I never really understood how this happened. that was early at the stage of learning Apex Cloth and I was not fully aware of the workflow. I never figured out why it happened and basically tried from scratch again (binding bones, painting max limits and so on)
Second, I noticed that I would get import errors, when I exported an apex file where my geometry was configured as you can see in the screenshot. I tried to do a curtain effect including the rings where the curtain is attached. UE would display an error text that it could not load the Apex file, so in the end and after quite some time of looking for the error I solved it, by changing the geometry that the rings had a small gap, so that there was not penetrating geometry left.
