Hard drive Ejects itself while running ddrescue
I won't blame anything or body except a failing hard drive. There is a old trick where you place a defective hard drive in an ESD safe bag and store it in the freezer for a couple hours. Once the metal is cold through the bag then try accessing the files again. You might have luck without ddrescue (which I am not aware of or experienced with) and the drive might just show up in Finder. However if it doesn't or it keeps ejecting and remounting you could drive a different computer or send the disk into specialists for data recovery.

Cheers