Avatar Limbs locked in VR [works fine on PC]

Hello! My friend is experiencing really strange bent-limb issues with an avatar they’re creating; and we’re both stumped as to what could be causing them. These issues only occur in VR – the avatar works completely fine on desktop. Here’s their message:

Hello, I am trying to make an avatar for VRchat, and am having issues with the VR-headset side of things, and am unsure whether this is an issue I can fix in Blender.
Here are the examples of the base model behaving properly on PC but having limb issues in VR: (please ignore the tail, I know I need to calm it down).

As the above image shows, the model’s limbs become all bent and locked at the elbows.

Things I have tried that have NOT fixed it:
VRC limb scaling - both in-game settings and the Unity add-on.
Re-scaling the limbs manually in Blender.
Working in both A-pose and T-pose when creating the model in Blender.
Editing/rotating the axis of the armature in Blender.
Adjusting the T-Pose in Unity.

I am honestly ready to throw in the towel, as I have no idea what I am doing wrong.
I follow YouTube tutorials to the finest detail, yet no one else seems to have this problem!
I use a Quest 2 for VR, have a Windows PC for Blender modelling and rigging, and use Creator Companion & Unity for VRC projects.

Any and all help, pointers or ideas would be greatly appreciated!
Thank you.