Hi Giuliano,
this can be due different reasons. I make two example (there are many) that could (or could not) fit your case.
Every single day can have different prices based on the time interval selected by the user. E.g. if I select two days a day can have a price but if i select 5 days (containing the same days) I can have a different price for the two days I selected before. As you can imagine there are lot of combinations. So we try to get a daily medium price over an available time interval. It’s difficult to explain the the evaluation process. I only tried to make an example.
If the property you are looking for has the same price for all the 365 days (and you do not expect this) it could be for an update priority reason. Please send us an email at info@insidebnb.com with the specific property ID. I will look at that precise property and I’ll be back to you.

Thank you!