Default Slot won't play in Animation Blueprint Template

I have an Animation Blueprint Template, the only thing plugged into the output pose is the default slot. I have a blueprint using an Animation Blueprint that links this template. In the blueprint, if I try to play an anim montage it won’t play. If I however in the ABP Template add an input pose, plug it directly into output pose AND in the regular ABP plug a default slot node into the input for the linked template, the montage plays.

Could someone please help me understand why this is happening? I need the default slot in the template to work because I am using it to blend the lower body movement from a running animation and the upper body movement from an attacking animation. Thanks!

Have you found a solution to this?

Nope, still looking for one.