WARNING: I just had to tweak the volume configuration again. Due to the Meltdown/Spectre kernel updates, all my Ubuntu 16.04 machines updated to kernel 4.13. Apparently that changes some part of the CIFS/SMB behavior as a client. I was getting really odd errors where files would appear with ls, but if you tried to read the file you would get a “file not found” error. The solution was to add the vers=1.0 extra option to the option strings in the above volumes. At least so far this seems to be working.