It's not a matter of 'making excuses', it's going after low-hanging fruit, first.
Any firearm is part of a 'system', comprised of the gun, the shooter, the ammo (and magazines, if applicable).
If a problem is not readily and obviously identifiable, it makes sense to modify what can be modified locally (as in, at owner's discretion, vs. sending back to mfr.), to see if problem responds to systemic changes.
Change a mag, change shooter, change ammo. Easy and quick. Did one change eliminate the problem?
Could it be the gun? Of course, but doesn't it make sense to check the easy stuff first, before sending it off for weeks?