Nextcloud not working because Redis is down

The file /var/log/redis/redis-server.log exists, but is empty. in the directory are no other files.

systemctl restart redis brings

Job for redis-server.service failed because the control process exited with error code.
See "systemctl status redis-server.service" and "journalctl -xe" for details.

systemctl status redis-server.service returns:

* redis-server.service - Advanced key-value store
 Loaded: loaded (/lib/systemd/system/redis-server.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Sun 2020-05-03 15:26:25 UTC; 28s ago
     Docs: http://redis.io/documentation,
           man:redis-server(1)
  Process: 13238 ExecStart=/usr/bin/redis-server /etc/redis/redis.conf (code=exited, status=1/FAILURE)

May 03 15:26:25 nextcloudpi systemd[1]: redis-server.service: Service RestartSec=100ms expired, scheduling restart.
May 03 15:26:25 nextcloudpi systemd[1]: redis-server.service: Scheduled restart job, restart counter is at 5.
May 03 15:26:25 nextcloudpi systemd[1]: Stopped Advanced key-value store.
May 03 15:26:25 nextcloudpi systemd[1]: redis-server.service: Start request repeated too quickly.
May 03 15:26:25 nextcloudpi systemd[1]: redis-server.service: Failed with result 'exit-code'.
May 03 15:26:25 nextcloudpi systemd[1]: Failed to start Advanced key-value store.