Yeah I tried it without internals in the upper and it still stops right after the barrel drops, the sharpie trick came back clean too, no marker rubbed off, I’m starting to wonder if the rear rails are messed up, cause one side is slightly high but it isn’t causing the slide to stick aggressively either and a 19.3 racked back fine on it, this is just getting weird at this point.
Are you sure you have the right barrel / locking block combo parts?