Normally I did the Extroot configuration, should it be enough ? What is weird is that once I unplug/plug the device it works as expected. For what is worth I just saw the device restart while it had factory settings and come back to my settings !

Here is the output of df -h and free -h:

root@GL-X750:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root                10.8M     10.8M         0 100% /rom
tmpfs                    60.3M    288.0K     60.1M   0% /tmp
/dev/sda1                14.5G    422.3M     13.4G   3% /overlay
overlayfs:/overlay       14.5G    422.3M     13.4G   3% /
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sda1                14.5G    422.3M     13.4G   3% /mnt/sda1
/dev/mtdblock6            3.1M      3.0M     88.0K  97% /rwm
root@GL-X750:~# free -h
              total        used        free      shared  buff/cache   available
Mem:         123584       63112       39028         160       21444       28188
Swap:        262140        2312      259828

I dont think its a power problem as Power led is on, and then again the device it works as expected if I unplug/plug it again.