@glenngould OK so you have the latest scrub fixes. I’ve just tried a freshly scheduled scrub here on 3.9.1.5 and all was OK:
What is the output of the following command:
btrfs scrub status /mnt2/pool-name-here
You could try removing that scrub job and re-creating a new one to see if that helps. All depends on what version that job was created on, ie those created before 3.9.1-2 will error out as they use the old pools api ie:
and:
Hope that helps.