Failed to start MariaDB 10.3.22

Nextcloud version (eg, 18.0.2): 1.26.2
Operating system and version (eg, Ubuntu 20.04): Raspbian GNU/Linux 10 \n \l
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 7.1):
Device : RaspberryPI 4 B 2Go + USB external HDD

The issue you are facing:
MariaDB service down… again.

Is this the first time you’ve seen this error? (Y/N):
No
I first install my NextcloudPi server in April it worked fine until end of may. The server went down with no apparent reason. I identified the issue with the help of research and another topic on this forum : the Mariad DB service is down. But despite a lot of research and an open subject on another forum I couldn’t get a fix. So I reinstalled the server from scratch in june and the same problem as before occurred yesterday.

Steps to replicate it:
I don’t know if it’s possible to replicate it since I didn’t do something particular before it happens

Step by step tutorial followed for the installation (in French) :
https://info.rueducoq.fr/demarrer-nextcloud-avec-windows/

Content of NC-info :

NextCloudPi version  v1.26.2
NextCloudPi image    NextCloudPi_03-28-20
distribution         Raspbian GNU/Linux 10 \n \l
automount            yes
USB devices          sda sdb 
datadir              /var/www/nextcloud/data
data in SD           yes
data filesystem      ext2/ext3
data disk usage      19G/221G
rootfs usage         19G/221G
swapfile             /var/swap
dbdir                /var/lib/mysql
Nextcloud check      error
HTTPD service        up
PHP service          up
MariaDB service      down
Redis service        up
Postfix service      up
internet check       ok
port check 80        open
port check 443       open
IP                   192.168.0.X
gateway              192.168.0.1
interface            eth0
certificates         XXXXXXXXXX
NAT loopback         no
uptime               41min

When I ask the MariaDB status I have the following :

Warning: The unit file, source configuration file or drop-ins of mariadb.service changed on disk. Run 'systemctl daemon-reload' to reload units.
● mariadb.service - MariaDB 10.3.22 database server
   Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/mariadb.service.d
           └─ncp-delay-automount.conf
   Active: activating (auto-restart) (Result: exit-code) since Wed 2020-07-22 19:03:32 BST; 3s ago
     Docs: man:mysqld(8)
           https://mariadb.com/kb/en/library/systemd/
  Process: 28519 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=0/SUCCESS)
  Process: 28520 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=1/FAILURE)

DB variables :

Variables (--variable-name=value)
and boolean options {FALSE|TRUE}  Value (after reading options)
--------------------------------- ----------------------------------------
abort-source-on-error             FALSE
auto-rehash                       TRUE
auto-vertical-output              FALSE
binary-as-hex                     FALSE
character-sets-dir                (No default value)
column-type-info                  FALSE
comments                          FALSE
compress                          FALSE
debug-check                       FALSE
debug-info                        FALSE
database                          (No default value)
default-character-set             utf8mb4
delimiter                         ;
vertical                          FALSE
force                             FALSE
named-commands                    FALSE
ignore-spaces                     FALSE
init-command                      (No default value)
local-infile                      FALSE
no-beep                           FALSE
host                              (No default value)
html                              FALSE
xml                               FALSE
line-numbers                      TRUE
unbuffered                        FALSE
column-names                      TRUE
sigint-ignore                     FALSE
port                              0
progress-reports                  TRUE
prompt                            \N [\d]> 
quick                             FALSE
raw                               FALSE
reconnect                         TRUE
socket                            /var/run/mysqld/mysqld.sock
ssl                               FALSE
ssl-ca                            (No default value)
ssl-capath                        (No default value)
ssl-cert                          (No default value)
ssl-cipher                        (No default value)
ssl-key                           (No default value)
ssl-crl                           (No default value)
ssl-crlpath                       (No default value)
ssl-verify-server-cert            FALSE
table                             FALSE
user                              (No default value)
safe-updates                      FALSE
i-am-a-dummy                      FALSE
connect-timeout                   0
max-allowed-packet                16777216
net-buffer-length                 16384
select-limit                      1000
max-join-size                     1000000
secure-auth                       FALSE
show-warnings                     FALSE
plugin-dir                        (No default value)
default-auth                      (No default value)
binary-mode                       FALSE

Any help will be very appreciated ! I use Nextcloud related services daily but if I have to restart from scratch every month I might as well go back to Google tools :confused: