Just had 2 drives become disabled, rebuilt them and then the same thing happen again after a reboot with different drives. This was my issue and I don't think I would have found it if you hadn't posted this, so thanks! You've saved me countless hours of troubleshooting!
Due to the HBA only being an 8x and sitting in a 16x slot, the two sata cables if moved have enough force to pull the back of the card out the slot slightly while still being firmly attached at the front.