@Gillian166
We all get this from time to time, but for your last three or four booking guests to do this is indeed very odd. I wouldn't be surprised if something has changed, seeing as Airbnb has been messing around a lot with the IB settings (which they never mentioned to us until people started noticing and making a noise about), so who knows what else they have done...
I do remember a few years ago, Airbnb introduced a feature where guests could select a check in time from a menu. The problem with this, and the reason why a lot of hosts complained about it, was that it didn't take into account the actual check in window of the listing. So, even if a listing specified check in between 3 and 10pm, for example, the menu would give guests the option of selecting 12pm. I wonder if they have reinstated this, or something similar. I hope not, as that would be very bad news.
I am not planning any trips in the near future, otherwise I would check, but perhaps someone else here is and can let us know what they see RE check in during the booking process.
By the way, were these all instant bookings?