New clients cannot run backup

I have had my UrBackup server running smoothly for many years, however recently I have tried to add new clients and they are not able to successfully backup. Old/existing clients are still running just fine.

Server: Debian 12 (Bookworm) / UrBackup 2.5.33.0
Clients: Windows 11 x64 / UrBackup Client 2.5.25

The error message is always:
Creating directory "/mnt/urbackup-data/(Client Name)/(Timestamp)/" failed. File exists (errorcode=17)

I can see the folder does exist, and it even looks like a few files were backed up successfully before the job errors out.

In my environment, /mnt/urbackup-data/ is an NFS share on a separate TrueNAS box. It has always been this way, however, even when initially setting up my server and configuring all the existing working clients.

Server log contents in debug mode (end portion where the job fails):

2025-06-22 17:45:34: Waiting for file hashing and copying threads...
2025-06-22 17:45:49: LMDB: PUT clientid=19 filesize=2621440 hash=UahvaVy7AEusFgkpuSeJpQ== target=154930073
2025-06-22 17:45:49: LMDB: PUT clientid=19 filesize=713728 hash=obMpfo+bxsOnoTOE4wijcA== target=154930078
2025-06-22 17:45:49: LMDB: PUT clientid=19 filesize=655360 hash=uoZJGmSMqMJ5S8oe/AMCKg== target=154930079
2025-06-22 17:46:27: Saved metadata of 28 files and directories. 15% done...
2025-06-22 17:46:27: Writing new file list...
2025-06-22 17:46:27: All metadata was present
2025-06-22 17:46:27: Syncing file system...
2025-06-22 17:46:27: Transferred 813.666 MB - Average speed: 885.282 MBit/s
2025-06-22 17:46:27: Script does not exist urbackup/post_full_filebackup
2025-06-22 17:46:27: Time taken for backing up client ChrisPC: 1m 22s
2025-06-22 17:46:27: ERROR: Backup failed
2025-06-22 17:46:27: Updating statistics...
2025-06-22 17:46:27: Updating image stats...
2025-06-22 17:46:27: Updating file statistics...
2025-06-22 17:46:27: Done updating statistics.
2025-06-22 17:46:28: msg=WAKEUP
2025-06-22 17:46:28: WARNING: Exponential backoff: Waiting at least 40m before next file backup
2025-06-22 17:46:28: server_prepare_hash Thread finished (exit)
2025-06-22 17:46:28: server_hash Thread finished - normal

EDIT: Initially listed wrong server version

I think I can mark this as resolved (though still unexplained).

We had a power outage today thanks to the brutal heat. After crossing my fingers and bringing everything back online, backups are now running just fine. Not sure if my UrBackup server or NAS needed to be rebooted, but the ‘File exists’ error hasn’t happened and my new clients were able to successfully complete their first full backup.