This is the worst detachable magazine system I've ever seen, next to the older Browning BLR pot metal magazines. On both of my 700s with DM, I have issues with the bolt not catching the rounds AT ALL to chamber them, usually with the first round in the mag. One 700 did it on most all the rounds. The mag was hanging too far down at the back.....the stupid retention system is placed midway and acts as a fulcrum, with spring pressure forcing the back down making it hard to chamber rounds. Your case sounds like the opposite, and almost sounds like bad magazines or feed rails. Good luck with Remington fixing anything right......I had one 700 back 4 or 5 times on a similar issue, and I paid most of the shipping. Do let us know how you resolve it.
RR