So we added 4 new hosts to our 10 host cluster and suddenly the existing hosts are showing this error:
The vSphere HA agent on this host cannot reach some of the management network addresses of other hosts, and HA may not be able to restart VMs if a host failure occurs:
31/07/2019 2:38:57 PM
So my guess is that this is happening since we added a new Backup VLAN to the hosts. This backup VLAN has the "Management Traffic" checkbox checked and this is causing the error. I assume that VMware is seeing 2 Management VMKernels, one in the Management VLAN and one in the Backup VLAN and it is confused as to which one to use for management traffic.
If this is the case then is it possible to "tell" VMware to use one VMKernel for management traffic amongst hosts and the other specifically for Backup traffic?