I noticed this was happening for my listings, too - even when I do a normal search without dates. I called Airbnb, and they told me they display listings that don’t have a lot of bookings to “give them a chance” when showing search results without dates, even on the map. So if you are pretty well booked, you won’t show up at all, even if you have upcoming openings. Results are displayed normally only when specifying dates.
This seems so backwards to me, sometimes I wonder if it is just an excuse, when in fact the real reason is that it is a bug that they are ignoring.