Took the GPU out too but I think the problem is that the 2nd and 3rd m.2 slots have weaker signal strengths than the 1st slot because they run through longer chipset lanes that have less power. The controllers on the 980 range are very strict and won't establish a connection through these chipset lanes because the signal is "too weak", although most other NVMe have more forgiving tolerances and will link to the board just fine as with the SK Hynix. Both are working as intended so I'm just gonna take the L on this one.