My Mac Mojo DX is set up in Slot 3 with a x4 lane width.
I have an ATTO fiber card in slot 4, again, x4 lane width
Slot 2 is empty and Slot 1 is my graphics card which must be x16.
Your lane width allocation is all wrong and you should have the Mojo DX connected before powering up, not after.
Not trying to be rude, but are you really surprised that it’s not working when you deliberately set it up contrary to Avid’s specification?