/dev/mapper/<volume> is not a device mapper device. Cannot snapshot via dm

Hi, Uroni!
I need help for the following weird behavior about my urbackup local installation.
UrBackup Server v2.5.31.0 installed on a Linux Mint 21 server. UrBackup Client Controller v2.5.25.0 installed on a Linux Mint 20.3 client. Server and client reside into the same local (private) lan.

Server is configured to periodically execute both backup-image and file-image of aforementioned client.

On client-side, snapshotting mechanism via dm has been activated during client-installation.
As a conseguence, root file system has been converted to be managed from dm.

Data files are instead archived into separate lvm-based volume, normally mounted on boot.
Here is the extract of /etc/fstab config file (client-side):

/dev/data_group/data_volume /media/data ext4 defaults 0 2

Image-backups processes work flawlessly, while file-backup after (more or less) a week of correct jobs executed using dm snapshotting mechanism, start to show on logs the following problem:

2023-10-24 00:29:45(info): Starting scheduled incremental file backup…
2023-10-24 00:29:47(error): Creating snapshot of “/media/data” failed
2023-10-24 00:29:47(error): Snapshotting device /dev/mapper/data_group-data_volume via dm…
2023-10-24 00:29:47(error): /dev/mapper/data_group-data_volume is not a device mapper device. Cannot snapshot via dm.
2023-10-24 00:29:47(info): Backing up “data” without snapshot.

The only workaround i’ve at the moment found is to reboot the client to make dm snapshotting mechanism restart to work flawlessly.
In the meantime, started to check lvm-based unit status to search for some errors. found only one, the following (command used is: ~$ sudo lvm lvdisplay)
WARNING: Device mismatch detected for data_group/data_volume which is accessing /dev/mapper/data_group-data_volume-a31725acca86421d-clone instead of /dev/sdb1.
— Logical volume —
LV Path /dev/data_group/data_volume
LV Name data_volume
VG Name data_group
LV UUID OyXWny-fsAy-SvXu-ATgW-DyXn-SV1V-CR6sp5
LV Write Access read/write
LV Creation host, time pc-XXXXXX, 2023-08-31 19:16:26 +0200
LV Status available

open 1

LV Size 120,00 GiB
Current LE 30720
Segments 1
Allocation inherit
Read ahead sectors auto

  • currently set to 256
    Block device 253:0

This is instead the extract of " mount | grep /dev/mapper" command:
/dev/mapper/root-98d1f8b1f435 on / type ext4 (rw,relatime,errors=remount-ro)
/dev/mapper/data_group-data_volume on /media/data type ext4 (rw,relatime)
command " mount | grep /dev/data_group" outputs nothing…

As you can see, the original “/dev/data_group/data_volume” device doesn’t exist anymore…