It's an error, he sometimes has the Omnitrix from Alien Force, then his Ultimatrix, back and forth
I don't believe so. I believe that Humungosaur (orginal) pretty sacrifices his growth ability for the enhancements of his ultimate form (Larger form, stronger, blaster hands, etc.) Pretty much the concept of evolution behind the Ultimatrix. Sacrificing one ability for further improvement of one's self.
Ye But That Means Ultimate Humungousaur Should Be Stronger Then Humungousaurs Largest Form But He Was Struggling With A 100(I Think) Robotic Humungousaurs
Yeah but he still held his own. They were all jumping at him at the same time and he still managed to defeat some of them.
probbaly, but can reboot humungousaur grow