Well, for starters, I don't think it was stated Goku stopped receiving zenkais after the Frieza arc. Sure, he didn't seem to get stronger after being near death, but I think he did get stronger but it was too small to be noticeable.
Anyways, I think it was more like Zamasu getting used to Goku's body. And maybe him being a god or something made the zenkais exaggerated. It's also why instead of getting Blue, he has rose.
I mean, correct me if I'm wrong, but can Goku black use god KI?