Linux client stops running


I have two Ubuntu linux clients that stop backing up without any obvious reason.
When I check I can see the client software has stopped running.
They are both internet clients running 2.0.36
I have a third, local, linux client running the same OS that runs fine.

The local client uses LVM for snapshots. The internet clients do not use snapshots but both show messages that say ERROR: Creating shadow copy of XXXXXX failed.
Is the error normal when not using snapshots ?

I have upgraded to various URbackup Server versions. So I don’t think it’s relevant.

Any help would be greatly appreciated.