VM - disk read-only after failed backup

[Herman]

Hi all,
I recently added a PBS backup to an existing Proxmox installation.
This installation has been running for years backing up to a NFS share on a Synology.
There is a single VM running zentyal (ubuntu 20.04), that I am not able to backup up to PBS.
The backup fails:

NFO: starting new backup job: vzdump --mailnotification always --mode snapshot --all 1 --notes-template '{{guestname}}' --node pve02 --mailto itsupport@xxx --storage PBS01
INFO: Starting Backup of VM 106 (qemu)
INFO: Backup started at 2023-01-06 20:41:40
INFO: status = running
INFO: VM Name: zentyal
INFO: include disk 'scsi0' 'local-lvm:vm-106-disk-0' 512G
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: creating Proxmox Backup Server archive 'vm/106/2023-01-06T19:41:40Z'
INFO: issuing guest-agent 'fs-freeze' command
INFO: issuing guest-agent 'fs-thaw' command
INFO: started backup task '85d25757-3cf1-4a60-bcea-a488a88b5693'
INFO: resuming VM again
INFO: scsi0: dirty-bitmap status: created new
INFO:   0% (196.0 MiB of 512.0 GiB) in 3s, read: 65.3 MiB/s, write: 57.3 MiB/s
INFO:   1% (5.2 GiB of 512.0 GiB) in 33m 4s, read: 2.6 MiB/s, write: 2.5 MiB/s
INFO:   2% (10.2 GiB of 512.0 GiB) in 54m 51s, read: 4.0 MiB/s, write: 3.9 MiB/s
INFO:   3% (15.4 GiB of 512.0 GiB) in 1h 19m 53s, read: 3.5 MiB/s, write: 2.7 MiB/s
INFO:   4% (20.5 GiB of 512.0 GiB) in 1h 58m 34s, read: 2.3 MiB/s, write: 2.2 MiB/s
INFO:   5% (25.6 GiB of 512.0 GiB) in 2h 47m 28s, read: 1.8 MiB/s, write: 1.7 MiB/s
INFO:   6% (30.8 GiB of 512.0 GiB) in 3h 13m 37s, read: 3.4 MiB/s, write: 3.3 MiB/s
INFO:   7% (35.9 GiB of 512.0 GiB) in 3h 38m 6s, read: 3.6 MiB/s, write: 3.5 MiB/s
INFO:   7% (38.7 GiB of 512.0 GiB) in 4h 6m 43s, read: 1.7 MiB/s, write: 1.6 MiB/s
ERROR: backup write data failed: command error: protocol canceled
INFO: aborting backup job
INFO: resuming VM again
ERROR: Backup of VM 106 failed - backup write data failed: command error: protocol canceled
INFO: Failed at 2023-01-07 00:48:24
INFO: Backup job finished with errors
TASK ERROR: job errors

Not only is the backup failing annoying, I still have the old backup that works without a problem, but after the backup the disk is read-only and when I reboot the instance, it goes to initramfs, I need to fsck /dev/mapper/zentyal--vg-root -y, where it repairs a bunch of errors, before it starts again.

Any ideas?

Herman