SetMasterPoseComponent messes up my mesh

I imported a character (really, just the head) from CC3 and assigned it to an existing skeleton. When I open the mesh, the mesh looks great and my preview animations look fine.

I make the head a meshcomponent to a blueprint character’s mesh, and in the construction script I call SetMasterPoseComponent to set the main mesh as the head’s master bone component, the eyes/tongue/teeth get misaligned with the rest of the head. Any idea what would cause this?

Missing weight paint?