Somehow, all my bookings for April 2019 have changed date to 2020. I believe that they are bookings imported from Air BnB.
I have only just noticed this today when someone tried to make a booking and they told me it was showing that it was already booked. I knew there were no bookings for that date, so I investigated further.
Unfortunately the dates are not editable, so unless you have a solution, I will have to delete them all.