How can i fix this broken animation?

Hello, as you can see on the youtube video, the animations with the items of my game are strange (especially at the level of the arms) with my character. On the other hand the animation is perfectly normal with the custom rig. The animations broke suddenly about 2 months ago. I have already tried to redo the animations, it’s the same problem with the arms. Do you know if there is a solution?

In the video you can easily see the difference in the arms between my character and the custom rig. Thank you