Vertices collapse on themselves So, I'm rigging a model and I noticed a problem with the Arm. As shown in the pictures, the upper part of the arm collapses on itself when I move it. The rest of the arm is fine. 

I'm still learning how to properly rig and such, so if anyone can tell me why this is happening, that would be greatly appreciated.
Here is the Blend file, i managed to get the head and somewhat of the left arm and still kind of new to rigging so it's not the best. I'm rigging it for vrchat so.
https://drive.google.com/file/d/12SQNEksYcoQCIxSNnqGwRWLvLGupZK4y/view?usp=sharing
It happens because one or several bones are influencing this part of your mesh when they should not.
Select the armature in Pose mode, shift select the object, switch to Weight Paint mode, select the bone called Chest, you'll see that its vertex group contains vertices that are part of the arm:

So in the N panel, choose Blend &gt; Subtract in order to remove these vertices from this group and it will work fine:

You could also shelect these vertices in Edit mode, go in the Properties panel &gt; Object Data &gt; Vertex Groups list, in the dropdown menu on the right of the list select Remove From All Groups, then assign to the group called Arm_L only.