Other mistake: When Omega Red brings the nuclear submarine to launch depth, the underwater cliff he parks it on is the exact same cliff where the submarine was originally located. (00:03:30 - 00:15:10)
Other mistake: After Omega Red stabilizes the nuclear sub while it is moving, the military somehow has a live video feed from outside the sub despite the fact that they didn't send any other submarines out to monitor the mission. (00:09:00)
Answer: Chris Potter, the original Gambit voice actor, did indeed quit the role in the 4th season. His last episode was The Phalanx Covenant Part 1 so it seems reasonable that Fox would limit the use of the character even though it was recast. It doesn't appear that Potter left the role due to animosity, he stated in an interview that he wished to play Gambit in the first live action X-Men film.
BaconIsMyBFF