I believe you were referring to page 25 of the manual in your post, quote:
Installation Notices for the M.2 and SATA Connectors:
The availability of the SATA connectors may be affected by the type of device installed in the M.2 sockets. The M2M_SB connector shares bandwidth with the SATA3 2, 3 connector. Refer to the following table for details.
Both the quote above and the images in the manual indicate, that only the M2M_SB NVMe port shares bandwidth with SATA3, Port 1 and 2. The other NVMe ports do not share bandwith with the SATA 3 ports. Besides, if there's no SATA port used in the system, does the M2. slot still share the bandwidth, or it can have it all?
My second Samsung 980 is connected to M2P_SB M.2 slot, that does not share bandwith. The sequence of the M.2 slots might be messed up, either in the manual or in the BIOS.
The M.2 slots are in somewhat increasing alphabetical order from the CPU down:
M2A_SB: next to the CPU
M2M_SB: second from the CPU
M2P_SB: third from the CPU
M2Q_SB: fourth from the CPU
Based on the BIOS, the first and third M.2 slots have the 980 Pros, but they were intalled into the first and second M.2 slots. By now, I know that was wrong, but why the BIOS report it wrong?
I'll try to move around the the second 980 Pro to see, if the bandwith changes.I don't like the heatsink over it anyway, instead of improve cooling, it seems to prevent cooling instead.