How are the cards installed? I looked through manual and dont see any way to control the two long slots to be x4 instead of primary x16. Wondering if you go all risers and use onboard video does it not see the 5th card? and also try on all riser with onboard off and video off card cabled to e1 (primary slot)?
Then just make sure you have VDT disabled, any m.2 not used should be disabled. Try turning off everything not needed (audio/cpu low power states/virtualization etc). Fast boot diasbled. Windows or Linux?
Also i assume you have tested all cards and work with risers just not with 5th installed. And confirm it boots with 5 cards but only sees 4...or refuses to boot with 5.
Many questions
Board should do it...manual even references crypto mining in 4g section with more than 4 gpus.
