As you can see below, there is a filter on field PM konec smlouvy 

however, you can see, that in this subset, there is a blank row and rows, which date is not in 3 months. 

What are you going to do about that pipedrive team :) ?

 

I asked the support, we were able to identify, that when you delete date and the field is blank - in the database stays actualy 0000:00:00. Which I still do not understand why it is in the filter. Maybe I am just missing some understanding.