All fixed. Weirdly even though the server had been rebooted it was a service stop / start that ended up resolving this. At least now I can push on with 10.1.3 installation.
Odd that it was just disk volumes that weren't polling but other data was fine
How was it fixed? We have experienced the same problem, but no matter what we do we cannot seem to remanage the devices. Deleting and adding solves the issue, but that is unacceptable as it causes the loss of all historical data.