Packaging Results in Map file size Explosion

I’m packaging using UnrealFrontend on a github’d 4.7.1 for Win64. I’ve taken the 3rd person sample template and replaced the static mesh.

Before Packaging, looking in the content folder:
ThirdPersonExampleMap.umap: 27,374 KB

After packaging:
ThirdPersonExampleMap.umap: 226,728 KB

That’s almost 10x growth!?

I’ve looked through the frontend log but nothing is jumping out at me. I poked around the .umap file in a hex editor and it looks like a sparse file with repeated data fields, lots of identical content and lots of empty bits.

I’m guessing the problem is some funky referenced asset, but how do I find which one? Can someone teach me how to dissect this problem further to find the root problem? What logs do I need to look at, what tools can I use? The map plays fine otherwise.

I’m also seeing this in an unmodified Side Scroller project.