My cloud mirror: HDD 1 LED displays solid red, but find nothing wrong in dashboard. What's wrong?

My cloud mirror: HDD 1 LED displays solid red, but find nothing wrong in the dashboard: Under home tab - Devices - Diagnostics shows Healthy, Storage - RAID shows “Healthy” and “All RAID Volumes are active and healthy”, Storage - Disk status shows “Healthy” and both drives are “Good”.

What’s wrong in this case?

Something is wrong, perhaps a HDD failure or overheating. If temperatures are reasonable then I’d be inclined to run a full system check for starters.

Temperature is around 40C. Full test is completed successfully. But HDD 1 still shows solid red light. Really weird.