I had a similar mag jam issue across a half dozen 10-round mags when my rifle and mags were new. What I did was fully load them all and let them sit that way for a couple of weeks and the problem went away. I had read about, and loaded the mags the 'correct' way both before and after this btw. I now store them loaded as well and I don't have the problem ever. Fed bulk #745 runs fine in mine..

Doing the same thing also fixed the same problem in some new metal 5 round mags I got for a win mod 69 bolt 22. I assume it helps the mag springs settle in a bit..

Dave