Mesh stuck in reference pose in Animation Blueprint

I have a skeletal mesh rigged to the default UE4 Mannequin skeleton (from the RifleAnimsetPro on the Marketplace). When I open the skeletal mesh, I can view the mesh animating just fine

If I create an animation blueprint using this skeleton, I can view animations on the default SK_Mannequin without issue.

However if I switch the preview mesh to my imported skeletal mesh, I only get the reference pose. What is wrong with my skeletal mesh?

If someone could point me in the right direction it would be greatly appreciated!

The same thing has happended to me, did you ever manage to solve this?