In the tournament between Universe 6 and Universe 7, Goku fights Frost, Frieza's good doppelganger. Goku powers up to Super Saiyan God Super Saiyan, but it is the traditional yellow instead of blue. Why is that?
He turned regular Super Saiyan because he's too sympathetic. He thought Frost was a 100% good guy, making Goku think Frost deserved to win. So he purposely fought at his base Super Saiyan form. I think he thought Frost was the exact same power as Frieza and would require minimal effort. Also because the writers are leaving out a great deal of details.
Goku and Vegeta are saving their true form for the final battles.
But after Goku lost it was discovered by Jacco that Frost was cheating and exposed who he really is. Which is a bad guy. A "War Profiteer."
So Vegeta asks Piccolo to forfeit so he can fight Frost rather than Frost being disqualified. It then showed Frost's hidden weapon being removed in next episode preview. And Vegeta is a base Super Saiyan as well.
Goku wasn't Super Saiyan God 2. He was just Super Saiyan.
It all comes down to plot holes.