backup failed: /mnt/vzsnap0//data failed: exit code 2

[dom6770]

Using PVE 9.0.10 and PBS 4.0.15 and ZFS as backend for PVE:

INFO: starting new backup job: vzdump 108 --mode snapshot --notes-template '{{guestname}}' --remove 0 --notification-mode notification-system --node Asgard --storage backup-pbs-local
INFO: Starting Backup of VM 108 (lxc)
INFO: Backup started at 2025-10-01 16:53:30
INFO: status = running
INFO: CT Name: minio
INFO: including mount point rootfs ('/') in backup
INFO: including mount point mp0 ('/data') in backup
INFO: found old vzdump snapshot (force removal)
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: suspend vm to make snapshot
INFO: create storage snapshot 'vzdump'
zfs_mount_at() failed: directory is not emptyumount: /mnt/vzsnap0/data: not mounted.
command 'umount -l -d /mnt/vzsnap0/data' failed: exit code 32
INFO: resume vm
INFO: guest is online again after <1 seconds
ERROR: Backup of VM 108 failed - command 'mount -o ro -t zfs zfs-storage/subvol-108-disk-data@vzdump /mnt/vzsnap0//data' failed: exit code 2
INFO: Failed at 2025-10-01 16:53:30
INFO: Backup job finished with errors
INFO: notified via target `stalwart`
TASK ERROR: job errors

With any other LXC it works just fine and the root fs also works fine, but I tried adding the second mount point (/data/), because I want to switch from Veeam to PBS, I cannot get it to work. If the LXC is offline, the backup starts, but that's not a solution for me. MinIO needs to be always reachable.

Storage:

❯ pvesm status --storage backup-pbs-local
Name                    Type     Status           Total            Used       Available        %
backup-pbs-local         pbs     active       821461504       420415616       401045888   51.18%
❯ cat /etc/pve/storage.cfg
dir: local
        path /var/lib/vz
        content vztmpl,iso
        prune-backups keep-all=1
        shared 0

zfspool: zfs-storage
        pool zfs-storage
        content images,rootdir
        mountpoint /zfs-storage
        sparse 0

pbs: backup-pbs-local
        datastore Main
        server proxmox-backup-server.home.lan
        content backup
        encryption-key [REMOVED]
        fingerprint [REMOVED]
        nodes Asgard
        prune-backups keep-all=1
        username root@pam

pct config

❯ pct config 108
arch: amd64
cores: 2
features: keyctl=1,nesting=1
hostname: minio
memory: 1024
mp0: zfs-storage:subvol-108-disk-data,mp=/data,backup=1,size=250G
nameserver: 192.168.144.254
net0: name=eth0,bridge=vmbr0,gw=192.168.144.1,hwaddr=[REMOVED],ip=192.168.144.108/24,type=veth
onboot: 1
ostype: debian
parent: vzdump
rootfs: zfs-storage:subvol-108-disk-0,size=5G
swap: 512
tags: community-script;object-storage
unprivileged: 1

Any help appreciated.