Unexpected Docker shutdowns

Hi,
I’m running Urbackup as Docker container (uroni/urbackup-server:latest) on openmediavault. Urbackup runs fine, but for unknown reasons it suddenly shuts down. I have the following log:


2020-12-09 07:53:10: New Backupclient: DE106TS7,
2020-12-09 08:05:24: Looking for old Sessions… 0 sessions,

2020-12-09 19:05:46: Looking for old Sessions… 0 sessions,
2020-12-09 19:08:51: Socket has error: 113,
2020-12-09 19:09:03: Socket has error: 113,
2020-12-09 19:09:16: Socket has error: 113,
2020-12-09 19:09:27: Socket has error: 113,
2020-12-09 19:09:40: Socket has error: 113,
2020-12-09 19:09:51: Socket has error: 113,
2020-12-09 19:10:04: Socket has error: 113,
2020-12-09 19:10:10: Client exited: DE106TS7,
2020-12-09 19:10:14: client_main Thread for client DE106TS7 finished,
2020-12-09 19:11:00: Client finished: DE106TS7,
2020-12-09 19:35:47: Looking for old Sessions… 0 sessions,
2020-12-09 20:05:48: Looking for old Sessions… 0 sessions,
2020-12-09 20:35:49: Looking for old Sessions… 0 sessions,
2020-12-09 21:05:50: Looking for old Sessions… 0 sessions,
2020-12-09 21:35:51: Looking for old Sessions… 0 sessions,
2020-12-09 22:05:52: Looking for old Sessions… 0 sessions,
2020-12-09 22:35:53: Looking for old Sessions… 0 sessions,
2020-12-09 23:05:54: Looking for old Sessions… 0 sessions,
2020-12-09 23:35:55: Looking for old Sessions… 0 sessions,
2020-12-10 00:02:12: WARNING: Shutting down (Signal 15),
2020-12-10 00:02:12: Exited Loop,
2020-12-10 00:02:12: Deleting at…,
2020-12-10 00:02:12: Deleting SelectThreads…,
2020-12-10 00:02:12: Deleting lbs…,
2020-12-10 00:02:12: Shutting down plugins…,
2020-12-10 00:02:12: Deleting server…,
usermod: no changes,

When I restart the container, the log looks like

2020-12-10 12:35:03: Starting HTTP-Server on port 55414,
2020-12-10 12:35:03: HTTP: Server started up successfully!,
2020-12-10 12:35:04: SQLite: recovered 11918 frames from WAL file /var/urbackup/backup_server.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 64017 frames from WAL file /var/urbackup/backup_server_files.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 8 frames from WAL file /var/urbackup/backup_server_link_journal.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 1 frames from WAL file /var/urbackup/backup_server_settings.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 11918 frames from WAL file /var/urbackup/backup_server.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 1 frames from WAL file /var/urbackup/backup_server_settings.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 64017 frames from WAL file /var/urbackup/backup_server_files.db-wal code: 283,
2020-12-10 12:35:05: SQLite: recovered 8 frames from WAL file /var/urbackup/backup_server_link_journal.db-wal code: 283,
2020-12-10 12:35:05: Started UrBackup…,
2020-12-10 12:35:05: Removing temporary files…,
2020-12-10 12:35:05: Recreating temporary folder…,
TEST FAILED: guestmount is missing (libguestfs-tools),
2020-12-10 12:35:05: Image mounting disabled: TEST FAILED: guestmount is missing (libguestfs-tools),
Testing for btrfs…,
2020-12-10 12:35:06: UrBackup Server start up complete.,
2020-12-10 12:35:06: Looking for old Sessions… 0 sessions,
2020-12-10 12:35:06: Server started up successfully!,
Create subvolume ‘/backups/testA54hj5luZtlorr494/A’,
Create a snapshot of ‘/backups/testA54hj5luZtlorr494/A’ in ‘/backups/testA54hj5luZtlorr494/B’,
Delete subvolume (commit): ‘/backups/testA54hj5luZtlorr494/A’,
Delete subvolume (commit): ‘/backups/testA54hj5luZtlorr494/B’,
BTRFS TEST OK,
2020-12-10 12:35:07: Backup destination does handle subvolumes and snapshots. Snapshots enabled for image and file backups.,
2020-12-10 12:35:07: Downloading version file…,
2020-12-10 12:35:07: Broadcasting on ipv4 interface eth0 addr 192.168.178.44,
2020-12-10 12:35:07: Broadcasting on ipv4 interface eth1 addr 192.168.178.57,
2020-12-10 12:35:07: Broadcasting on ipv4 interface docker0 addr 172.17.0.1,
2020-12-10 12:35:07: Broadcasting on ipv6 interface eth0 addr 2001:16b8:3f8d:8c00:230:48ff:fe91:882c,
2020-12-10 12:35:07: Broadcasting on ipv6 interface eth0 addr fe80::230:48ff:fe91:882c,
2020-12-10 12:35:07: Broadcasting on ipv6 interface eth1 addr 2001:16b8:3f8d:8c00:230:48ff:fe91:882d,
2020-12-10 12:35:07: Broadcasting on ipv6 interface eth1 addr fe80::230:48ff:fe91:882d,
2020-12-10 12:35:07: Broadcasting on ipv6 interface docker0 addr fe80::42:72ff:fef1:9a5d,
2020-12-10 12:35:07: Broadcasting on ipv6 interface veth85b542d addr fe80::d4a3:fff:fee1:e36c,
2020-12-10 12:35:07: Downloading version file…,
2020-12-10 12:35:07: Downloading server version info…,
2020-12-10 12:35:07: Downloading dataplan database…,
2020-12-10 12:35:38: New Backupclient: DE106TS7,

What forces urbackup to shut down?