Arms not attached to body

For the mesh that I use for my animations, the arms are attached to the body…

but when I play the animations from the Animation Starter Pack, the arms are not attaching to the body

I finished the animations before and had the arms attaching to the body. The arm sag didn’t start to occur until I retargeted the mesh, but I’m pretty sure that’s not what’s causing the issue. Does anybody know if this is a bug or am I doing something wrong? I can send more screenshots if needed.