My Book loses connection to My Cloud

I’m not sure where I should post this so if this is the wrong place please tell me where it should be or move it.

I have a 2TB WD My Cloud running as a NAS with a 3TB WD By Book plugged into it as a backup drive. I gave up on getting the WD software to back up the My Cloud on the My Book years ago and installed Karen’s Replicator on my main computer (win10) to do a file by file backup every night.

This worked perfectly for several years but I recently noticed that KR often reports a lot of failures and eventually figured out that when it reports those failures the My Book seems to have disconnected from the My Cloud.
Sort of.
If I browse to Network>WDMYCLOUD the My Book is in the list of folders (shares) as “My_Book_1230-1” and if I click it I see the folders listed as they should be but when I click one of them I only see 2 or 3 of the folders that should be in it.

I have found by trial & error that if I unplug the power supply from the My Book, wait until the drive stops and plug it back in (the only way I can find to re-boot it) the light on the My Cloud flashes for a while and then I can access the files on the My Book and KR can run the backup without errors.
But a day or 2 later KR lists multiple failures again and I have to repeat the process.

During all of this the light on the My Book glows dimly and sometimes flickers a bit (I don’t remember if it was brighter when I first got it - to be honest, once I had everything working I didn’t pay it much attention).

I don’t have a reference for it but it seems to me that I originally plugged the My Book into the My Cloud because that’s what was required to use the WD software for backing up the My Cloud to the My Book. In this case the My Cloud acts as a server computer on the network.

What makes you think the My Book’s drive is running 24/7? From what I can tell by feeling the case it only runs when the My Cloud communicates with it.

I bought the My Book specifically to use as a backup drive for the My Cloud (I believe I found that recommended by WD at the time).

I don’t know who you are, what your qualifications are or why your public profile is hidden but you seem to be intent on trying to tell me that my equipment can’t do what it has been doing for several years instead of trying to help me figure out how to overcome my current problem.

Perhaps someone who is actually interested in helping will reply.