Revealing mistake: McGarrett's office is on the 2nd floor. Yet the photo backdrops outside his windows in this episode show us a ground-level view of grass, streets and a building. This boo-boo vanishes in subsequent episodes, replaced with the more likely views of balconies, palm trees and blue sky. (00:08:00)
Continuity mistake: There's much too abrupt a transition between Reese falling into the water and his body suddenly being back on the dock. As there's no time lapse implied at all, he seems to reappear on shore by magic. At least a brief shot of the body being fished out of the water might have helped. (00:49:40)
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.