Weird deformation on animations

Hey guys, I am having issues with the animations on a model that I am trying to import, resulting in some really weird deformation. I have checked everything that I could think of, from rotations, scale, roll and I can’t find a single thing causing it.

What it should look like and what the base pose looks like:

What the animation looks like:
Screenshot 2024-09-12 150952

Anyone have any ideas what might be causing this or if I can change the reference pose to the base pose? Using t0 as ref pose also results in the weird deformation.