Tahnk You. It was running perfectly on 18.8.1 drivers with the same clocks/voltages. But only 6 GPUs were seen. So I don't think that it is clocks issue.
The miner is successfully finding and running all 8 GPUs in that screen shot. As for the error, the 'Failed to enqueue kernel' error means that something has gone very, very wrong with the driver, possibly due to cards crashing.
What clocks/voltages are you running on those cards?