CoW raw image backup on ZFS Linux 0.8

I have been sucessfuly usin Copy-on-Write on Debian Stretch for some time. Followed the setup instructions and no problems.

I have been trying a test setup with Debian-Buster which installs ZoL version 0.8. I though the inbuilt encryption feature would be useful, However even though the setup is identical to my existing setup on Stretch I cant get it to work. When I run “urbackup_snapshot_helper test” I get “TEST FAILED: Creating test zfs volume “Pool1/UrBi/testA54hj5luZtlorr494” failed” its identified the dataset correctly so I assume the problem is creating the test volume.

I am beginning to think there is something in the latest release of ZoL which has broken UrBackup but so far not found anything in my searches.

I am running server version 2.3.8. Anyone else hit this problem?