Errors After Moving Data from Windows Share to Unraid Share

I have recently moved to using Unraid as a central share for all our files previously using shares on a Windows box.

I run a URBackup client on a Ubuntu 18.04 server that backs up all these shares (this was installed with binary install with these instructions and datto block driver is installed too).

The shares were mounted with SMB using cif to access them. This had been working fine for the Windows shares but is giving a lot of errors with the Unraid shares. Although the backup copies do seem to be being made there are a lot of warnings and errors shown which could obscure a real error.

The server web page reports errors in the backup process

Errors 02/16/20 15:25 Snapshotting device //UNRAID01/Share via dattobd...
Errors 02/16/20 15:25 Using /dev/datto0...
Errors 02/16/20 15:25 driver returned an error performing specified action. check dmesg for more info: No such file or directory
Errors 02/16/20 15:25 Creating snapshot of "Share" failed.

There are 2 types of errors shown in /var/log/urbackupclient.log.

ERROR: Creating shadowcopy of "Share" failed.
ERROR: Error getting extended attribute list of file /home/backupuser/BackupMounts/"Share"/"somefile" errno: 5

The second error is shown for many (all?) of the files in the share.

As far as I can see the extended attributes are readable:

backupuser@UNRAIDBACKUP01:~$ ls -la /home/backupuser/BackupMounts/Share/somefile
-rwxr-xr-x 1 root root 146624 Jun 18  2019 '/home/backupuser/BackupMounts/Share/somefile
backupuser@UNRAIDBACKUP01:~$ lsattr /home/backupuser/BackupMounts/Share/somefile
----iadA-EjI------ /home/backupuser/BackupMounts/Share/somefile

The shares are mounted as follows (vers=1.0 added as I read somewhere this is needed for datto)

//UNRAID01/Share /home/backupuser//BackupMounts/Share cifs credentials=/home/backupuser/.smbcredentials,iocharset=utf8,vers=1.0 0 0

And this share is then configured to be backed up:

backupuser@UNRAIDBACKUP01:~$ sudo urbackupclientctl add-backupdir -f -d /home/backupuser/BackupMounts/Share
backupuser@UNRAIDBACKUP01:~$ sudo urbackupclientctl list-backupdirs
PATH                                   NAME     FLAGS
-------------------------------------- -------- ------------------------------
/home/backupuser/BackupMounts/Share    Share    symlinks_optional,share_hashes

Why are these errors being reported and what can I check next to fix them?

URBackup client is the latest Ubuntu release.
URBackup server versions are 2.3.7 and 2.4.10 (first is local local and second is remote via internet).
Issues are occurring on both versions.