For anyone referencing this thread in future, the answer turns out to be bang-my-head-against-a-server simple
Look in the summary tab - a relevant message can be there as well as the alarms tab. In my case, as follows:
'Configuration issues, vSphere HA initiated a virtual machine failover action in cluster'
Quick Google, and advice was, turn off HA and back on again - boom, problem solved
Didn't even need a Change Control ;-)
TGIF
thanks to all for input