Additive PoseAsset has strange stretching when applied to a mesh that adds bones when going from LOD 0 to LOD 1 [Metahuman-ish]

Hi! So I’m working with Metahumans but this problem isn’t necessarily a MetaHuman problem.

If I’ve got an additive PoseAsset with two poses set up in it, the poses work fine at LOD0. The problem arises when you move down a LOD.

In the metahuman facial structure, a bone is omitted from the mesh in LOD 0, called “FACIAL_Hair1”. This is specified in the LOD generation settings, but can be seen in the hierarchy with a greyed-out bone:

image

In LOD 1, this bone is introduced via the LOD settings:

image

And the additive pose goes from looking like this in LOD 0:

To this in LOD 1

And the culprit is FACIAL_C_Hair_1, as seen here:

I’m struggling to find the root of the problem, I’m thinking the base pose is only referencing the bones present in LOD 0, so when an extra one is added when moving to LOD 1, it doesn’t know what the additive transform is?

If anyone has experienced this issue or knows what may be the fix, I’d really appreciate any help!