So, I believe you issue is similar to the last time we approached this process. To layer materials on a single object, the composite approach you took is not the supported workflow. I noticed you did not have material id’s assigned to these UV’s which is why the FBX appears stretched and skewed.
This is the workflow we support and the compositing is not expected to work in the same manner without having first established material id’s for each unique material you are calling to render that is mapped to that object.
This is more than likely why neither your FBX or Alembic are rendering similarly and are showing different materials. I highly suggest taking a read over our documentation on multi-material objects to get and understanding of the workflow we support when exporting from Max or Maya into Unreal.
If you have further questions please let me know.
Thank you,