I have exactly the same problem, on a clean install of Bionic/18.04 Desktop AMD64, with a locally-attached (USB) 2TB SATA hard drive which works perfectly AFAIK for all functions other than Deja Dup.
I have exactly the same problem, on a clean install of Bionic/18.04 Desktop AMD64, with a locally-attached (USB) 2TB SATA hard drive which works perfectly AFAIK for all functions other than Deja Dup.