If the fit is loose enough to cause function issues,then yeah I'd say its a problem.Otherwise I'd let it rattle.Common wisdom is to avoid the wedges or o-ring fixes.If you want to try and tighten it up a bit,then get a set of Armalite NM pivot and take down pins and see what that does for you.
Otherwise if you have some other lowers try swapping uppers around to get the best fit between the bunch.Pretty much all my rifles are put together with mixed manufacturers receivers.Some fit kinda tight and some are kinda loose,same goes for the factory built guns..
Glock Certified Armorer
Armed Protective Services II
Bookmarks