For some reason your disk3 was shown in the smart folder of the diagnostics as unassigned so that is why I asked for the screenshot.
SMART for all mentioned disks (parity,disk3,14,15) looks OK, didn't look at the others. Do any disks have SMART warnings on the Dashboard page? I recommend dual parity for that many disks.
Disk3 has to be rebuilt of course. Do you know how to proceed?