I have same problem. I did try to re-enable Docker repo but no success. When docker gui installed with errors, through ssh apt-get update && apt-get upgrade and aptitude found badly installed packages
2 not fully installed or removed.
Do you want to continue? [Y/n] y
Setting up docker-ce (5:18.09.1~3-0~debian-stretch) ...
Configuration file '/etc/default/docker'
==> File on system created by you or by a script.
==> File also in package provided by package maintainer.
What would you like to do about it ? Your options are:
Y or I : install the package maintainer's version
N or O : keep your currently-installed version
D : show the differences between the versions
Z : start a shell to examine the situation
The default action is to keep your current version.
*** docker (Y/I/N/O/D/Z) [default=N] ? y
and seem that all works after install the package maintainer's version.