Brand new resource calendars can take up to 24 hours to sync before they allow full scheduling. Google has more info here.
In rarer cases, resource calendars may not continue to update apps like Robin when changes happen. This is a known issue, and you can read more on it here. Google is currently investigating this issue. If you think this might affect you, try creating a test resource calendar to see if it has different results.
If you're looking for help connecting your calendars with Robin for the first time, right this way.