@Stephen2120in the present system update, each night's minimum stay can be individually changed on the calendar. If you click a date and then custom settings, it changes the stay for only that night.
Also, when one changes things on the calendar, such as unblocking a "gap" night that was blocked before, the system often sends a pop-up saying that you have to reduce the minimum to one night to open it up. If you click OK, that specific night will have a one-night minimum.
Lastly, you can also check whether the minimum is perhaps set differently per day of the week (click through on the overall calendar minimum stay setting), or whether there was perhaps a rule applied with professional hosting tools (I think these two explanations are less likely in this case).
