Oskar went through this recently also. Just one day it was like a switch had been flicked and all of a sudden he didn't like bath time with daddy anymore. It had to be mummy.... then I started putting the shower on and that worked so I could transition him to bath on his own. I bought a new bath toy (Elmo wind up one only about $6) and that has made it better. Along with a few new jugs out of the plastics cupboard and usually bath time is happy again now. I think they just go through different stages as they grow but can't verbalise it to us so we are left scratching our heads. Hope it gets better for you.