Hi got some problems too with this board, 

I got one rig with 10 gpus (rx580, 560,  2 vega 56) - no problems at all.  all gen2, onboard graphic etc..

I mount another rig with 10 vega 64 but only can connect 9, if i installed the 10 gpu, i have no post on poweron..

Any ideia too what could i check?

I changed to 16 gb ram its the same, have a lot of power too..

No problems in risers too,

my solution was to put one vega in my desktop pc.. but its frustating

Regards,