Thanks a lot @meyay for your suggestion regarding the installation mode.
I hence proceeded to install docker directly from apt packages with the following commands, and as you can see at the end of this post, it now works correctly.
I don’t know what is actually different between those 2 installs mode, but this solved my issue for now.
sudo apt-get update
sudo apt-get upgrade
sudo apt install docker.io containerd
sudo systemctl start docker
sudo systemctl enable docker
so that now I have the following
$ sudo docker info
Client:
Context: default
Debug Mode: false
Server:
Containers: 10
Running: 9
Paused: 0
Stopped: 1
Images: 9
Server Version: 20.10.2
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Cgroup Version: 1
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
Default Runtime: runc
Init Binary: docker-init
containerd version:
runc version:
init version:
Security Options:
apparmor
seccomp
Profile: default
Kernel Version: 4.15.0-151-generic
Operating System: Ubuntu 18.04.5 LTS
OSType: linux
Architecture: x86_64
CPUs: 12
Total Memory: 62.69GiB
Name: jump.my-backend-server.com
ID: SZGV:VFSE:27QN:PJ3C:ZNFW:GXZU:VMSH:GQGP:V3SO:EINS:N72T:LDBX
Docker Root Dir: /var/lib/docker
Debug Mode: false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: false
WARNING: No swap limit support
and it works correctly why I report the df result 
sudo docker exec -it nodeexporter sh -c 'df -h /rootfs / /host /host/sys /host/proc'
Filesystem Size Used Available Use% Mounted on
/dev/md3 937.3G 39.1G 850.6G 4% /rootfs
overlay 937.3G 39.1G 850.6G 4% /
overlay 937.3G 39.1G 850.6G 4% /
sysfs 0 0 0 0% /rootfs/sys
proc 0 0 0 0% /proc