LED blinks at a slow breathing rhythm after a disk replacement

Dear all,
I replaced both of the HDDs in my WD My Cloud Home DUO after the original HDDs were full. Later I found that one of the new drives was a failed one, so I put both of the original HDDs back to the My Cloud Home DUO device. Then I found that the LED on the device keeps blinking at a slow breathing rhythm for days, and in my WD discovery program the device was offline. I do not want to reset my device, and is there anyone who knows how to fix this issue? Or is this issue normal? Very appreciate your inputs.

WD Tech support said “You cannot take both drives out”. So I guess there is no way to recover the data. Please make sure you do not take both drives out at the same time, and it is actually very difficult to truly backup your data since you cannot archive the drives in the device.