Only events that the synced calendar organises are synced
When you create a sync connection to a calendar, it will only sync events that are related to that calendar via a dimension field lookup. If you add reservations to the calendar via a dimension junction field lookup (e.g. you can relate multiple records to the reservation of this type). The sync connection will not sync these.
Sync Field Priority can cause fields to not sync correctly
When syncing into multiple external fields the field that will be the organiser of the events should have the highest priority. If it does not have the highest priority, any fields that have higher priority than the organiser field will be left empty.