Does anybody know what causes this and how to fix it? Trying to convert an XPS model to PMX but this happened, and I don't know what to do.
I think that happens when the waist and upper/lower body bone aren't parented properly.
Try to open a working model
and see how the bones are parented:
Mother bone <- Center <- Groove <- Waist <- Upper Body 1 & Lower Body
Since you are converting a model,
this could help you as well.
It's for FBX, but once you get any model into PMX,
the process of fixing it is pretty much identical for any conversion.
I'll take a look at it.