Hi @Kate-Spinks0
We don't sync to a Google calendar, but there have been some issues with the Google calendar and Airbnb calendar being off by one day since the Summer release, but not the situation you are mentioning? That is bizzare. The only think I can suggest is to delete the links between the two calendars and then resync them.
I would try syncing Airbnb to Google first, then Google to Airbnb. If that doesn't correct it, try the reverse (sync Google to Airbnb first, then Airbnb to Google).
Perhaps another Host who uses the Google calendar can advise?