I can add information that using a share on windows 10 as remote causes this error.
But using samba on linux with this config is ok:

[global]
  workgroup = BERG
  server string = ember
  security = user
  guest ok = no
  map to guest = Bad Password
  log file = /var/log/samba/%m.log
  max log size = 50
  printcap name = /dev/null
  load printers = no
  min protocol = SMB2
  ntlm auth = yes

[localNetwork]
  comment = Local Network Storage
  path = /mnt/storage/localNetwork
  browsable = yes
  read only = no
  guest ok = no
  valid users = local,john-arvid
  force group = samba
  force user = local

I can add information that using a share on windows 10 as remote causes this error.
But using samba on linux with this config is ok:

[global]
  workgroup = BERG
  server string = ember
  security = user
  guest ok = no
  map to guest = Bad Password
  log file = /var/log/samba/%m.log
  max log size = 50
  printcap name = /dev/null
  load printers = no
  min protocol = SMB2
  ntlm auth = yes

[localNetwork]
  comment = Local Network Storage
  path = /mnt/storage/localNetwork
  browsable = yes
  read only = no
  guest ok = no
  valid users = local,john-arvid
  force group = samba
  force user = local

@olivierlambert Has there been any progress on the VDI.snapshot? Read somewhere that there could be another branch for testing, but I did not find any.

I have tested with a clean install of xcp-ng with the latest patches. (Just to make sure it was nothing there causing a problem)
But the issue is still there.

@deoccultist Thanks for the reply.
I have tried all the steps that @julien-f suggested to you in the last post in your topic.
Guess I have to wait until they have something new I should try.

@julien-f Ok, understand:)
I missunderstood @olivierlambert "From XO" description. I ran that command from the xcp-ng server, and not from the XO server.

I ran it now and the ls command is successfull.

A next run does not fix the situasion.

vhd-cli check returns OK.
Do you want me to run the xo-backups clean-vms also?

@julien-f Do you mean that the remote is not mounted when a normal backup completes successfully but a Delta backup fails?
How can I go forward?

@olivierlambert Do you mean from xcp-ng?
ls: cannot access .... No such file or directory
There is no xo-server folder in /run/

But yes, the VDI that was mentioned in the error is working as expected.
Let me know if there is anything else I should try.

I will try to import it and check.
But does it matter? Normal backup works, delta backup does not.

Did another test now with the latest master.

Now I got another error message: EINVAL: invalid argument, open '/run/xo-server/mounts/93d6810c-711c-4c13-b5ba-9009f3d75933/xo-vm-backups/f8d7e336-57ac-5d98-7825-98c722ef927c/vdis/7e734662-59e8-45cd-a5e0-3abedeecf0dc/621d81e1-0ea2-4155-a7d4-0966b607fb60/20210409T130439Z.vhd'

Log file: 2021-04-09T13_04_30.972Z - backup NG.txt

FYI: While I did this test I also ran a normal backup from another xen-orchestra instance. The VM that I ran a delta backup on was not currently worked with by the normal backup.