push the pin out, with the hammer face facing right, rotate the spring clockwise until the U hits the rear of the hammer, put it in the lower with both arms pointing rearward and slide it forward into position with the receiver holes and hold in place while you push the pin in to position and see if it looks the same as the picture.
I'm wondering if he's doing something funky when he installs like unwinding one of the coils a rotation before installing in an effort to get a lighter pull
Another curious thing I'd check is that he has the disconnector spring under the disconnector and not the bolt latch spring. They are similar in size and can be swapped, but one works and the other doesn't.
I did this myself once and the gun worked...too good... but it's possible that it could hang things up.
Some elimination is to pull the known good trigger group out of the other AR and put it in this one and see if the problem repeats. If no, then the issue is with the FCG itself and not the lower. The pic almost looks like the hammer is canted to one side, but it could just be camera angle.
If the other FCG group works, try the disconnector spring from it and see if that eliminates the issue.
OK, range update. At the range this morning, second shot fired, the hammer spring jumped off and flew out the bottom taking the magazine with it. Just kidding, wanted to get your attention. Actually the gun performed perfectly. I ran about 40 rounds thru it and never a problem. I am gonna leave the hammer spring in as is and as long as it works ain't gonna mess with it. Thanks to all for your help. Wallace