Hello @Erin78,
When two calendars fail to synchronise it can be difficult to find which side is at fault.
When a HomeAway booking doesn't show, as you say by 4pm, has that booking been made that day or several days previously?
Calendar synchronisation can take several hours. In my case synchronisation between my Airbnb and Google calendars is done only once per 24 hours.
One thing you could try is to reverse the synchronisation direction.
Did you sync to your Airbnb calendar by importing the HomeAway one to it or did you log in to HomeAway and export its calendar to Airbnb?
If you imported the HomeAway calendar to Airbnb then you could try loging in to Airbnb and removing the HomeAway calendar.
Then go through the process of exporting the Airbnb calendar and importing it to HomeAway.
If you originally imported the Airbnb calendar to HomeAway then remove the Airbnb calendar from HomeAway and go through the process of exporting the HomeAway calendar to Airbnb.
If something like the above doesn't work, and since the problem seems to occur only in the specific circumstance of successive night bookings, the only solution might be to manually block your Airbnb calendar the moment you receive a multi night booking on HomeAway. Not ideal I agree.
Steve.