So VMware have admitted that the alert seen in vROps 6 for the below error and have a KB article written for it.
Unfortunately the resolution says to disable the DVPortGroup Dropped Packets alert, this turns out to be easier said than done.
As an alternative fix I have looked at the configuration for the Alert Definition to allow people to delete the current alert and re-create it if\when vROps 6.0.x comes out and the fix is present there.