When I weight paint to the Left Hand (weight 1) the results are wrong. Its like the character is in an A-Pose. When I do the same thing with the Right Hand everything is fine. Also, the mirror results from right to left seem in correct. Again, this is the only bone linked to these VERTS.
You can upload it to some cloud base storage and share the link. If you hesitate to share public at the thread, send me a PM.
Here is a link to the file:
Thanks
I suppose there was some unrecoverable error with this character.
I sent it to Blender with pipeline and back, which rectified it. Round trip can fix many errors with characters in CC.
Fixed a Bind-pose in Blender in a way (right leg was deformed in Bind pose).
And generally, when you make weight corrections, do it in Bind pose to avoid mesh movements.
Thanks… I can almost replicate the issue, but it seem to be a bit intermittent. Also, it might only be happening on the ultrawide. Basically:
a) go to skin weights
b) select the layer (jacket)
c) select the right hand bone
d) select vert mode
e) select the vertices at the end of the sleeve (char right side)
f) select change to t-pose
g) select wight of 1
Sometimes its wrong here. Oddly, if you select a weight 0 its also in the same spot. so they seems to be some kind of bug, but at least I can avoid it now. I’ll create a video if it because perfectly replicable…
Thanks for all the help… 
There might be a bug, that’s why I said it’s better work in Bind pose in most of the cases.
At the animation player select Remove > Restore Bind Pose before going into Skin Weights and do not switch to T-pose.
