qc is an ever present possibility, i can't see anything intrinsically wrong with any of those parts, but it's always the way with airsoft that even good parts might not work quite right for a given gun.
do you have a tappet plate delayer chip? if not worth installing one, it'll give the mag that little bit extra time to get a bb into the chamber before the nozzle closes.
what kind of issue? might be the rubber, as above sometimes an otherwise decent part can be weird if it ain't quite the right one for the gun.