I have an issue with an Embedded Linked Mode-topology wherein the main vCenter Server (and first to have been installed) has become extremely slow. All vCenter Servers are @ 6.5.0 latest build. VMHost servers in the cluster where the vCenter Server is served are all 6.5.
This has been working well for months now.
E.g. reconnecting a host, starting a service on whichever VMHost might take anywhere from 30 seconds to a full minute. However, when looking at the "Start time" and "Completion" time, only a second has gone by
Logging onto the vCenter Server takes forever, up to several minutes before it accepts the credential and loads the UI. Doesn't matter if it's PowerCLI, HTML 5 client or the Flash client.
I also checked that if I change a setting on a host in vCenter, even if the /task/ in vCenter Server takes tens and tens of seconds, the actual setting will be changed near-instantly (or within a second) on the host.
Inspecting vpxd.log reveals that there are thousands of "missed heartbeats" from hosts, but there are no drops in the firewall, and it even happens for the VMHost that hosts the vCenter Server-VM and other hosts in the same subnet, where there is no firewall.
In vpxd.log, tasks like "DoHostSyncTime" for hosts take upwards of 30 seconds (30000ms) or MORE.
Adding one of the hosts from the problematic vCenter to another vCenter, one of which is in the same cluster as the problematic one, in the topology goes instantly and everything works smoothly.
Tips for troubleshooting?