Plot hole: Nadira hides from the bad guy behind a screen - with her feet in plain view. Then, after capturing her, the bad guy inexplicably lets her go, even though her knowledge poses a danger to him. Given that he's killed without a qualm before, this makes no sense at all.
Continuity mistake: 12-17 "A Bird in Hand": We see Angie take photos of mobster Del Vecchi with a 35mm camera. But later on, she develops the same photos and says she took them with a 110 camera hidden in her purse. She's a professional photographer and would certainly know the difference between 35mm and 110 film.
Answer: He was fired. He never really appreciated his character. He felt Kono was portrayed as a big dumb Hawaiian and that the stereotype was racist. He also felt underutilized. He was fired after a heated argument with the show's publicist regarding his character. It seems there's not much details given regarding the incident or the firing, so it's seems possible he upset the show's producers as well.
Bishop73
No he said something derogatory about one of the Jewish producers that's why he was fired.