Does it have a hardware RAID card? You may have to flash it to IT mode. The ‘lost’ drive may be just a parity drive?
Personally, I just looked at my firewall’s logs on the WG port and the handshake info. Once you have a handshake I don’t think there’s much that can go wrong on the WG side, maybe there’s a problem with lost packets or network roaming?
Does it have a hardware RAID card? You may have to flash it to IT mode. The ‘lost’ drive may be just a parity drive?