Some calculated fields does not change

Hi guys !

I have a problem with my Opportunity module. So I have 2 custom fields: Category (which is a dropdown: H&S, ICT, TBD) and Reference (which is a calculated field).

The reference is a mix of some other data, the thing is: for some reason it only calculate the field reference when the category is TBD. But in my opportunity field (in the Studio) I have set no condition at all.

Does somebody know where the problem comes from?

Thank you already.

Soufiane