I've had issues. My MPX malf'ed yesterday which cost me a local club match win. it was a pcc match too. I'd say 150gr federal syntec ammo is the incorrect ammo for a MPX. They're gas guns and 150gr ammo doesnt make much gas...
regardless, ive had good luck with my MPX', but I've had issues too, like all PCCs. I have 3 MPXs tho. 1 practice gun, 1 match gun, 1 match backup gun.