AH01753: access check of 'localhost' to /index.php failed, reason: unable to get the remote host

Hi all,

my nextcloudPi installation worked like a charm for 1 year but since today the WebUI on port 443 is not accessible anymore and the sync client does also not work anymore.
I can access the console WebUI who says: Nextcloud check :error

The apache2 log says:

AH01753: access check of ‘localhost’ to /index.php failed, reason: unable to get the remote host

The mariaDB server can also not start with the following msg:
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 10.3.17 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: failed (Result: timeout) since Sat 2020-02-29 18:48:50 CET; 40min ago
Docs: man:mysqld(8)
https://mariadb.com/kb/en/library/systemd/
Process: 573 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=0/SUCCESS)
Process: 589 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=0/SUCCESS)
Process: 604 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] && VAR= || VAR=/usr/bin/galera_recovery; [ $? -eq 0 ] && systemctl set-environment _WSREP_START_POSITION=$VAR || exit
Process: 758 ExecStartPre=/bin/sleep 20 (code=exited, status=0/SUCCESS)
Main PID: 1048
Tasks: 14 (limit: 4154)
Memory: 79.5M
CGroup: /system.slice/mariadb.service
└─1048 /usr/sbin/mysqld

févr. 29 18:32:09 nextcloudpi systemd[1]: Starting MariaDB 10.3.17 database server…
févr. 29 18:32:52 nextcloudpi mysqld[1048]: 2020-02-29 18:32:52 0 [Note] /usr/sbin/mysqld (mysqld 10.3.17-MariaDB-0+deb10u1) starting as process 1048 …
févr. 29 18:45:50 nextcloudpi systemd[1]: mariadb.service: Start operation timed out. Terminating.
févr. 29 18:47:20 nextcloudpi systemd[1]: mariadb.service: State ‘stop-sigterm’ timed out. Skipping SIGKILL.
févr. 29 18:48:50 nextcloudpi systemd[1]: mariadb.service: State ‘stop-final-sigterm’ timed out. Skipping SIGKILL. Entering failed mode.
févr. 29 18:48:50 nextcloudpi systemd[1]: mariadb.service: Failed with result ‘timeout’.
févr. 29 18:48:50 nextcloudpi systemd[1]: Failed to start MariaDB 10.3.17 database server.

All occ commands are also failing:
sudo -u www-data php occ -V
An unhandled exception has been thrown:
Doctrine\DBAL\DBALException: Failed to connect to the database: An exception occurred in driver: SQLSTATE[HY000] [2002] No such file or directory in /var/www/nextcloud/lib/private/DB/Connection.php:64

[/details]

Nextcloud version: 17.0.3.1
Operating system and version : Raspbian GNU/Linux 10 (buster)
Apache or nginx version : Apache/2.4.38
PHP version: 7.3.11-1

Could somebody advice me to solve this issue and get my nextcloud instance working again?

Many thanks in advance.
Blairy