Had a brief search of the forum but didn't have any luck.
First I apologise if I'm fundamentally 'doing it wrong'.
Before we bought XI I stood up Nagios Core as we didn't have a great deal of confidence in our previous solution. In addition to Nagios Core, I added NagiosQL as I wanted it to be easily maintainable by staffers that may be afraid of text based configuration files.
Using NagiosQL I was able to relate services to host groups and then populate those host groups with hosts so we could have a good baseline of monitors quickly and easily. I could then cherry-pick whatever hosts/services I wished into service groups to provide a decent 'at-a-glance' overview of the 'important bits' that provided a particular functionality to the business.
As exporting this config to XI results in a huge mess, I'm basically starting over from scratch using the above methodology. I've found however that I can't relate hosts/services to a service group where those hosts/services already have a relationship.
Service group from Core:

Service group config from NagiosQL:

Service group config from NagiosXI - only host services that have been explicitly created (i.e not inherited via a host group) appear:

We're running the latest update of the software but this is also in the previous iteration. Is there any way around this issue, or is this working as intended?