maybe extra plastic?
i am using one at the moment with the new shell and have no problems
maybe your motherboard is not inserted or placed all the way up inside the shell?
The molds are slightly different, there is an additional "bar" on the orange backplate between the FPGA (U1) and whatever chip U2 is, that's not there on the black backplate. However, that bar seems only to be separating the two chips as a means of reducing "side-to-side-wobble". I might try taking that out with a dremel later.

But when assembling with both the black and orange backplate and looking into the cartridge, I can't notice any difference between the two on how the board is seated.
So for now, I'm just using my "frankensteined" shell with the black backplate. Once it's inserted in my GBA, you can't really see the black backplate anyway.
