MariaDB docker keeps restarting - only rebooting ubuntu helps (for a while)

Hello, for some reason the mariadb docker container keeps restarting since monday morning.

To be precise:

docker ps
CONTAINER ID        IMAGE                   COMMAND                  CREATED             STATUS                          PORTS                                            NAMES
c8bffec3a8a3        nextcloud               "/entrypoint.sh apac…"   32 hours ago        Up 20 minutes                   127.0.0.1:8080->80/tcp                           nextcloud
aa596350c1b6        mariadb                 "docker-entrypoint.s…"   32 hours ago        Restarting (1) 54 seconds ago                                                    nextcloud-mariadb
d9d240954209        instrumentisto/coturn   "docker-entrypoint.s…"   32 hours ago        Up 20 minutes                   0.0.0.0:3478->3478/tcp, 0.0.0.0:3478->3478/udp   nextcloud-coturn
2429513d7a98        redis                   "docker-entrypoint.s…"   32 hours ago        Up 20 minutes                   6379/tcp                                         nextcloud-redis

After starting nextcloud without -d:
This is the response after docker-compose -up:

nextcloud-mariadb | find: '/var/lib/mysql/mysql': Input/output error
nextcloud-mariadb exited with code 1

One thing is very interesting though:
I seem to get the same error, when trying to access the mysql folder inside my mariadb directory:

But the confusion became even greater when I could enter the directory but not read it:
grafik


Update

I already got this error a few weeks ago. Deleting the containers didn’t help, but restarting my ubuntu server helped. I also managed to solve the immediate symptoms by restarting. So my Nextcloud is running (for now). But since i don’t know where this is issue came from, it will surely return.

Does someone have a clue how i could investigate this further?

Nextcloud Details

Nextcloud version : 20.0.1
Operating system and version : Ubuntu Server 20.04.1 LTS
Apache or nginx version : Server version: Apache/2.4.41
PHP version : PHP 7.4.11 (inside the docker container)
PHP version : no php (outside the docker container)

Is this the first time you’ve seen this error? (Y/N): N