Admin page unavailable after cancelled backup job & hard reboot, shares are working

Hopefully someone can help me get out of this deadlock.

I recently added a rsync backup job to sync the local /media share with an USB drive that was connected via the rear USB socket of the RN214 box. After starting it, I found out that - by mistake - the NAS was creating a directory /media/media/... on the USB drive (essentially duplicating all my data), so I cancelled the backup job via the ReadyNAS admin page. After refreshing the page I was presented with  the progress bar and eventually a notification similar to the one described in https://kb.netgear.com/26883/ReadyNAS-OS-6-Admin-Page-is-offline. A graceful restart did not work, the LCD was not lighting up. So I pulled the plug, forcing a cold restart.

After this, the device came back up again, however boot progress notification is stuck at 95%, the upper line of the LCD says "fvbackup-q.servi". I can ping the device and the shares are accessible (RW). Unfortunately the admin page http://rn214/admin/ is still offline (same error as mentioned above), the power button never stops blinking.

I have not set up SSH access (dammit!), so I can't log on and view logs/running processes. NetGear RAIDar reported the management service to be offline and was unable to retrieve logfiles. Diagnostics yielded the snippet below (slightly abbreviated, there were a lot more entries saying "Failed to UPDATE dictionary".

I can reboot the device using RAIDar. In that case no progress bar is shown at all (only "Booting...") and the "fvbackup-q.servi" information if the power button is pressed once. Shares are available, admin page says "Connecting..." and then ends up with the offline notification mentioned abov.

Any advice on how to proceed?

Many thanks in advance!

Successfully completed diagnostics
System
No errors found.
Logs
2021-09-22 11:34:39: Assertion 'f' failed at ../src/journal/journal-file.c:1674, function journal_file_post_change(). Aborting.
2021-09-22 11:02:36: ufsd: "mount" (sda2): is mounted as NTFS at 2021-09-22 09:02:36
2021-09-22 11:00:19: ufsd: "umount" (sda1): is unmounted at 2021-09-22 09:00:19
2021-09-22 07:26:17: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-22 05:26:17
2021-09-22 07:25:57: ufsd: "umount" (sda1): is unmounted at 2021-09-22 05:25:57
2021-09-22 07:25:37: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-22 05:25:37
2021-09-22 07:20:02: ufsd: "umount" (sda2): is unmounted at 2021-09-22 05:20:02
2021-09-22 07:19:50: ufsd: "umount" (sda1): is unmounted at 2021-09-22 05:19:50
2021-09-22 07:19:31: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-22 05:19:31
2021-09-22 07:19:12: ufsd: "umount" (sda1): is unmounted at 2021-09-22 05:19:12
2021-09-22 07:18:02: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-22 05:18:02
2021-09-22 07:17:16: ufsd: "umount" (sda1): is unmounted at 2021-09-22 05:17:16
2021-09-22 07:05:39: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-22 05:05:39
2021-09-22 01:01:17: ufsd: "umount" (sda1): is unmounted at 2021-09-21 23:01:17
2021-09-21 07:44:33: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-21 05:44:33
2021-09-21 01:00:57: ufsd: "umount" (sda1): is unmounted at 2021-09-20 23:00:57
2021-09-20 10:22:24: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-20 08:22:24
2021-09-20 10:22:06: ufsd: "umount" (sda1): is unmounted at 2021-09-20 08:22:06
2021-09-20 10:19:31: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-20 08:19:31
2021-09-20 10:18:29: ufsd: "umount" (sda1): is unmounted at 2021-09-20 08:18:29
2021-09-20 08:13:42: ufsd: "mount" (sda1): is mounted as NTFS at 2021-09-20 06:13:42
2021-09-03 09:55:17: ufsd: "umount" (sdc1): is unmounted at 2021-09-03 07:55:17
System Management
2021-09-22 11:37:21: Failed to UPDATE dictionary
2021-09-22 11:37:21: Failed to UPDATE dictionary
2021-09-22 11:37:03: Failed to start ReadyNAS System Daemon.
2021-09-22 11:36:43: Failed to start ReadyNAS System Daemon.
2021-09-22 11:36:17: DB (main) schema version: new ==> 24
2021-09-22 11:36:17: DB (queue) schema version: new ==> 0
2021-09-22 11:36:16: DB sanity check failed! Trying backup readynasd_2021_09_22_110945.db.lz4.
2021-09-22 11:36:16: DB sanity check failed! Trying backup readynasd_2021_09_22_110945.db.