Hi @Player_003 sorry to hear that you are running into this problem. I think we can fix this with a simple solution. All you’ll have to do is make use of “additive layers” and reposition the finger rotation. This fix should also apply to other errors that may pop up when retargeting an animation. Here is a post where I go over them. Although the problem in this answer was the orientation of the character, you should still be able to apply the same fix to your problem and bake out a cleaned-up animation, if however, you are still running into problems please let me know and I’ll see how I can help 
Here is the answer I referred to previously: