Only events that the synced calendar organises are synced
When you create a sync connection to a calendar it will only sync events that the calendar is the organiser for. You can have other events synced but only if the organisers have a sync connection.
Sync Field Priority can cause fields to not sync correctly
When syncing into multiple fields the field that will be the organiser of the events should have the highest priority. If it does not any fields that have higher priority than the organiser field will be left empty.