I had an issue like this once, drive would not even show up in disk management. What I did was, went into disk management, and changed the drive letter for every disk in there made them F,G,H,I and it solved my issue. I'm not sure why this worked, only thing I could think of was, the new M.2 wanted the same drive letter as one that was already assigned a letter, I would have thought Windows disk management would have sorted this all out, but it didn't. This may not be your issue, but I guess you could try it, I was surely surprise this happened.