relationship cross filter direction

Hi

I don't undertsand this behaviour in my model. I have this relationships

One Oferta can have many Ofertantes but could be records in Ofertas than they are not yet in Ofertantes obviously and so on I select cross filter direction single.

If I don´t add any fields of Ofertantes in my report I have records until 17-04-2017

But when I add to my report the BajaMedia field of Ofertantes in my report disappear many records. All the records of february, march and april

and followed when I examine the relationship again it shows like this other way

Any idea please?

regards