I wouldn't worry yet given the last update before September was in June. Update could just be taking awhile I would not start to worry till February
I would say it’s okay to start worrying a little. Just looking back at the releases of the content updates it’s usually a 2-3 month wait between each. That being said, I think giving the creator the benefit of the doubt would be better cause of Christmas potentially messing up the work schedule, and the next content update potentially being bigger than previous ones due to it being worked on for longer.