I’m having this same problem. I don’t believe it’s an actual faulty drive. I went ahead and replaced both drives since I’ve had this mycloud mirror since around 2014, and… the day after replacing the drives, the red light for Drive 1 came on again.
I am, however, able to get it to clear after full scan (…takes 2 days…) and then rebooting. But, a day or so after, it will return. Rinse and repeating the scan and reboot shows no issues. I’m suspecting a problem with a recent update, but can’t confirm.
Any advice on how to solve would be much appreciated.