OK Katie, here is a story...
Your MD export is perfectly fine (obviously). CLO is not so.
The easiest way to identify a problem, is to open all 4 in Blender, check vertex count and then try to see where the problem is.
The vertex count for each pair FBX/ABC MUST match.
Here is your MD export pair in Blender (I had to scale ABC object to 0.01 to have them side by side). Vertex count matches. No problem here.
Now CLO, I checked and found that ABC export is short for a little over 200 vertices compare to FBX. This would never import to iClone.
So I start checking where the difference is coming from. And here it is.... ABC file is missing Buttons. I cannot tell you where they are :)
I do not even know what to tell you to check, but it is definitely a CLO problem and not the iClone issue.
If you do not know/have Blender at all, you can verify in iClone, but it is a little harder to identify where the problem is. This is how:
Import FBX, then select nothing in Scene Manager and import respective ABC. It would be imported separately as an object.
Select each and check poly count at the top left corner. If there is a mismatch, try visually check what is missing.
Then go back to your app and try to figure out what the problem might be with the export.