I verified that it was just that ammo by using 2 different AR's (one 16" one 20"), 10 different mags, and 5 other types of ammunition during two separate range sessions. In all cases only the AE 50 gr would cause a short stroke - about 50 % of the time. The severity was different for each box from the same case, i.e. one box would fail 100% and the next would fail 25%. Anyone else have problems with this ammo?

Nope, never.  Put about ~2,500 rounds of it down range.......