If a calendar channel (Airbnb, VRBO, etc) is importing both myfrontdesk's calendar and one from another site, they will override each other.
Having two different sources exporting availability info through an iCal URL into a calendar channel will cause conflicts.
This is because each time Airbnb syncs and pulls data from either external calendar, it will set its availability using the info from the most recently updated calendar. This is similar to how having two PMSs connected to myallocator creates conflicts.
When setting up Airbnb or VRBO, make sure that myfrontdesk/myallocator is the only calendar that channel is importing availability information into.