I suppose that tolerance stacking could account for an occasional combination of different manufacturers’ components not being compatible.
It was an Anderson BCG with a poor match to a Bear Creek barrel. The Bear Creek BCG worked fine. I like Anderson's lowers and hadn't considered a possible mismatch with a Bear Creek barrel. Easily resolved. When I want a more finished product, I use Aero Precision upper/lower/handguard components. I also put a Yankee Hill Machine dust cover on the upper with the barrel caliber/cartridge laser engraved to avoid mistakes e.g. putting a 300BLK in a .223.