Did a parity check last night which returned 0 errors. Just rebooted and running SMART extended self-tests now. Will update with additional findings. Thanks!
So I came home earlier and noticed this error had popped up while I was out. Tried running both SMART short self-test & SMART extended self-test on Disk 2 but clicking on the START buttons of either tests don't seem to do anything. Should I stop the array first? Not sure what the correct steps are to remedy this issue. TIA!