[graphdriver] prior storage driver aufs failed: driver not supported

I am running a website on Docker on a Ubuntu platform (Ubuntu 18.04.1 LTS). For some reason, following system upgrade my docker won’t start. It shows the following error:
[graphdriver] prior storage driver aufs failed: driver not supported

I have tried many things recommended in here or other places. For example: - https://forum.manjaro.org/t/no-aufs-in-kernel-4-14/35371/9 - removed/reinstalling docker-ce

Following Docker-ce reinstallation I get the following message

update-alternatives: using /usr/bin/dockerd-ce to provide /usr/bin/dockerd (dockerd) in auto mode
Job for docker.service failed because the control process exited with error code                                                    .
See "systemctl status docker.service" and "journalctl -xe" for details.

When I run journalctl-xe, I can see the following error message

Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.004229379-05:00" level=info msg="systemd-resolved is running, so using resolvconf: /run/systemd/resolve
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.008851952-05:00" level=warning msg="failed to rename /var/lib/docker/tmp for background deletion: renam
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.010988609-05:00" level=info msg="parsed scheme: \"unix\"" module=grpc
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.011180824-05:00" level=info msg="scheme \"unix\" not registered, fallback to default scheme" module=grp
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.011774151-05:00" level=info msg="parsed scheme: \"unix\"" module=grpc
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.011936628-05:00" level=info msg="scheme \"unix\" not registered, fallback to default scheme" module=grp
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.014725816-05:00" level=error msg="AUFS was not found in /proc/filesystems" storage-driver=aufs
Dec 21 03:34:56 ultraball2100 dockerd[2984]: time="2018-12-21T03:34:56.015058973-05:00" level=error msg="[graphdriver] prior storage driver aufs failed: driver not supported"
Dec 21 03:34:56 ultraball2100 dockerd[2984]: Error starting daemon: error initializing graphdriver: driver not supported
Dec 21 03:34:56 ultraball2100 systemd[1]: docker.service: Main process exited, code=exited, status=1/FAILURE
Dec 21 03:34:56 ultraball2100 systemd[1]: docker.service: Failed with result 'exit-code'.
Dec 21 03:34:56 ultraball2100 systemd[1]: Failed to start Docker Application Container Engine.
-- Subject: Unit docker.service has failed

I cannot purge everything as I am afraid to lose my website data.

Any idea on what I could do?

Thank you