What motherboard BIOS version is currently installed?
Have you tried the drive in the M2_2 slot?
Have you checked the BIOS to see if there are settings to enable the slots that are not connected to the CPU as the M2_2 and M2_3 slots are fed lanes by the chipset rather than the CPU like the M2_1 slot is. This is doubtful, as I didn't see anything in the manual, but worth checking I guess. Likely this is either a bad drive, bad slot or BIOS issue.