M.2 boot up problem

[cadmunkey]

Been running my system for a while with a Samsung 970 Evo plus as my boot drive, and decided to get some additional storage so opted for 2x Corsair MP510's. Bought the Akasa Dual M.2 PCIe SSD Adapter to mount the Corsair drives on, but when installing it my PC refuses to boot from the 970 and asks for a legitimate boot drive. Works perfect again when removing the adapter, anyone any ideas why? Motherboard is an MSI X99A Mpower so a couple of years old now.

 

[bremen1874]

Is the adapter taking PCIe lanes that the M.2 slot requires?

Are all the drives visible in the bios?

 

[cadmunkey]

Is the adapter taking PCIe lanes that the M.2 slot requires?

Are all the drives visible in the bios?

Good point about the PCIe lanes, I'll move it around and see.
Strangely my 970 has never been visible in my BIOS, and I cant see the MP510s either.
Cheers.