J.B.
I would get him evaluated pronto. I have a son with autism, and that is one way that can manifest. They have skills and are verbal, and then lose them. It may be a phase, but if it is not, the sooner the treatment starts the better. For what it's worth, my son always said dada and never mama. And I was the one with him all day. But more attached to me to the point that he could not be left with anyone else, except his Dad and grandparents.