Not to get too far afield, but how different are the internals of a 9mm MP5 and a 10mm MP5?
Was that a major reengineering, or "just" a heavier bolt and springs?
The 10mm is going to be closer to a 40S&W in case and bolt face dimensions--and is MUCH more powerful than a 9mm. The lowers are set up to the same presentation of a Glock magazine--IMO you cannot necessarily expect the 10mm to feed in the same way or as reliably as the 9mm. Case support issues are the same as they would be in a pistol for the 10mm--but now your basically "swatting" the cartridge in from a Glock mag that is not "presenting" the cartridge close to the chamber face--and it's going in at an exaggerated angle at that. You need that big carrier mass to perform alignment duty when the angled cartridge meets the exaggerated radiused chamber opening--sorta like a big forcing cone on a revolver.
Until the "slavery" to the idea of a pistol cartridge AR MUST use Glock mags interchangeably with pistols--these fundamental issues will never go away IMO. If someone can point out even ONE LE or military unit that uses a 10mm Glock and AR where this is mandatory--I'd sure like to hear about it.