Part of animation starts shaking in unintended ways when imported to Unity

Here's a video of the issue. Animation is fine in Blender, but shaky in Unity. I also tried reimporting the fbx file into Blender and it's fine animationwise. I am using Unity 2018.3.12f1.,Title says it. I have an animation from Blender and when I export it to fbx and into unity, one of the hands start shaking like crazy while also twisting the rig a little making the elbow look strange. There's a video of the issue down below. I also tried importing the fbx file back into Blender and animationwise, everything is fine! I am using 2018.3.12f1 as my version.

 

Ok, apparently, I fixed it by importing the same fbx file, but fresh, under a new name. This new file is working, for some reason.

 

What's the difference between the two files? Can you check?

 

None, as far as I am aware. My guess is that the problem was caused by multiple rig modifications in the mesh during the project. I can't think of anything else.