Did you try their warranty first?
You almost have to have a small burr on the trigger bar release. Any way to dress the two parts with a very fine stone?
I would try breaking the edge, so you don't have a sharp edge if you have not already. If the two metals are equal in hardness and you have a burr or it's sharp , you will get a burr. Both surfaces could be flat at rest but when cocking, it could be tipping slightly, creating a sharp edge.
Just break the edge, your not looking to remove very much.
Good shooting!