One suggestion from the Rookie. I do not have an M&P, but did have a Rem R1. (Traded it in part for a 625) When it was new I had some challenges feeding. I saw a blurb on the internet that suggested leaving the magazine full to "work the spring" (paraphrasing for lack of memory on the topic), so I stored the magazines with 5 rounds in both of them. I ended up not shooting the R1 for several months and when I did, it shot flawlessly for the several hundred rounds I put through it before trading it. I was using 200 SWC reloads. Initially failure to feed happened with the 200 SWC reloads I made and a white colored box of Winchester 230 ball ammo. (my reloads were all tested in a Go-NoGo gauge, so they were pretty good as far as size specifications.)

If you have not done so, you might try storing the mag with 5-7 rounds in it to see if it helps. I would be very careful of manipulating the feed ramp or any surface. From my reading, it's the biggest mistake many owners make with 1911's (I know it's an M&P, but...)