MyBook 500gig Keeps unmounting and mounting itself

MyBook usb 500gig keeps unmounting and mounting itself.

I’ve tried the following:

Different USB ports on same computer

Different USB ports on different computer

Removed drive from casing an put in another enclosure

I’ve run disk utility and it says the drive has no errors

I’m at a loss as to how to proceed. I must get the data off this disk.

Suggestions?