I see where EC was coming from, but to further think about the OP's problem he had....what if the mag catch was the part that was out of spec? It obviously solved his issue, so is it possible that was the bad part? Maybe. What if there was a tolerance stacking issue between all of the Frankenstein parts we use to build these rifles? Could both Pmags actually have been within Magpul's specs? Could the one that worked actually have been the "bad" one?
Point is, nothing in this world is truly a bolt together system. Especially in the large frame AR world. Look through this forum, that forum, take your pick....nothing but many guys experiencing issues. Some of them are very experienced guys having issues. In a perfect world all we would be here for is to BS and brag about the parts we bolted together. Sure there's plenty of that, but when you can solve an issue by trying out an inexpensive part that someone else has already learned "might" fix your problem....it's worth a shot