I have no direct knowledge of, and have never handled, the "new" R51.
However, the problems with the Remington 51 go back to the original. Remington had to find a way around some Browning patents on the locked breech mechanism, so what they came up with was a buffered blowback design. The design was complex, very sensitive to parts tolerance and cleanliness, and very sensitive to ammunition parameters. The Model 51 was designed by John Pedersen (of "Pedersen Device" for the '03 Springfield fame).
I strongly suspect that the designers of the R51 sought to bring forward this buffered blowback design (for historical reasons; the Browning patents having long since expired). They may well have gotten a "working prototype" to work, but as anyone in this business knows, there is many a slip between working prototype and production examples. Chambering the pistol for 9mm (versus .32 ACP and .380 ACP for the Model 51) only complicated matters further.
If you want an all steel, single stack, carry-sized 9mm, there are better designs of proven reliability. The SIG P239 is one.