Flipping pose isn't working when I copy a pose (ctrl + c) and then flip it with this shortcut(shift+ctrl+c) the I see some weird result don't know why.



then this happens after I've pasted it



You can check the blend file if you want. I've uploaded it in my google drive.
Your bone "Arm.R" have wrong rotate.

So,simply to fix it you should delete this bone and all hand bone and add new bone by symmetrize from left side.