@RSNTeam -
I *just* posted a network issue we are having in 6.5U1 here: Odd Network Issues Since Migrating Environment From vSphere 6U3 > 6.5U1
Can you read my post & see if you are having similar? Not all VMs have a network issue or show as 'down'. I think it's mostly communication than 'down' type stuff. Although, we have had a VM be not pingable (glad this part is rare). What we noticed is this seems to be solely when VMs run on vDS and not vSS. Curious to hear your issue.
Thanks.