@Heidi762
Your calender shows all potential bookings starting before 31 januari must end at latest 31 januari (date set to: check-out only)
Bookings starting after 31 januari have not such a maximum.
Is your calender synchronized with a calender on another booking-platform ?
Try to remove the check-out only status set on 31 janauri and test if it solves problem
If problem can not be solved, then try to make an initial reservation to 31 januari.
After confirmation the reservation should be extended ("change" option on the reservation) with the remianing time period, by the guest or the host.