OMIVV 4.3 timeout on vCSA 6.7 U1

We have OMIVV deployed and linked to 4 vCenters. On some vCenters, the plugin times out when loading any of the relevant panels such as the "OMIVV Cluster Information" panel. We just get a "Loading..." response. Eventually the error below pops up in vCenter...

The query execution timed out because of a back-end property provider 'com.dell.pg.spectre.inventoryservice.ServerLockdownStatusPropertyProviderImpl' which took more than 120 seconds.

or

The query execution timed out because of a back-end property provider 'com.dell.pg.spectre.inventoryservice.ServerOEMPropertyProviderImpl' which took more than 120 seconds.

or

The query execution timed out because of a back-end property provider 'com.dell.pg.spectre.inventoryservice.ServerOverviewPropertyProviderImpl' which took more than 120 seconds.

and

A Web server communication error occurred; wait a few moments for the communication to automatically reset. If the communication does not reset, check the appliance IP address setting to make sure it is on the network. If the appliance is on the network, perform a reboot. If the error still occurs, contact Technical Support.

Are there any tweaks or optimizations we should make to our environment? We have a mixture of ESXi 6.5 and 6.7 hosts.