vCenter shows all VMs and Host is disconected

Hello,

I have a two node cluster running ESXi6 U2 (recently upgraded from 5.5) on hp dl380p gen8. For some reason all VMs are running on host A (HA and DRS are enabled).  vCenter shows all VMs and Host A is disconnected. Can't login to Host A using vSphere client or web client.Can't vMotion the VMs. Can't enable SSH. DCUI login works fine. Can't perform any VM action  

All VMs are up are running at this stage. I don't want to restart the VMs. Can you please help me ?

Thanks,

AJ