Any ideas on how to solve this issue? Basically, when I rotate this bone very slightly (or significantly), the mesh twists like this.
I think you messed up the roll on ur bone. You may be able to fix it by pressing ctrl a and applying location, scale and rotation. But you may have to unparent the bones from the mesh first then reparent them.
I agree. Looks like the sort of thing that happens when you don’t apply scale and rotation to the mesh and the armature before parenting.
Thanks for your responses! It was indeed an issue with the bone roll (I just had to recalculate the roll along the X axis).