Glad it has worked out and good job GM. Someone help me out please because I really like knowing cause and effect. OP stated that it appeared the pin holes of the trigger / hammer were "too low towards the trigger opening .....". Now that all the smoke has cleared, the very thin shim had to have elevated the trigger / hammer. Too low / too high could have caused difficulty with pin alignment possibly resulting in the mechanism being torqued / wedged off any given axis to the point of malfunction.

1. The pin holes of the receiver were actually lower, possibly offset as well ,from the mechanism pin holes. Right?

2. Haven't messed with the 15-22 however any AR (within spec) I've seen has a small space, greater than the Timney shim thickness, between the fire control group and the bottom of the well. Typically when installing either a stock assembly or a module - style aftermarket assembly, the assembly is raised a bit to vertically align its holes with the receiver holes.

Once again, glad to see it squared away. Just looking for the precise cause of the misalignment. Up or down of the assembly pin holes? Thanks.