Curious as to what type of lube you're using on your slide, also what is your shooting environment? If its cold and you're using grease rather than light oil, it could explain your FTF's and no slide lock-backs.

I've experience that myself with my plastic M&P's and was warned against using heavy oil in some target pistols (specifically not to use grease in a a SIG P210A). That said, I've got both a new and old M41's in which I exclusively shoot SV (SK+) ammo and have not experienced failures as you've described. I hope that you get it sorted out. -S2