When a service is linked to a xpandmon monitor which has already discovered all the nodes, the existing servers (dynamic nodes created by xpandmon) don't seem to be added to the service. This causes the service to have no servers in it.
With a monitor like this in the configuration:
and with a service created like this:
If xpandmon has already discovered all nodes, the servers won't be added to the service and as a result, it behaves as if it had no nodes. A workaround to this is to unlink and link the bootstrap server to the monitor.