The Phoenix Saga (1): Sacrifice - S3-E3
Other mistake: When Dr. Corbeau opens the door to the locker room, Cyclops, Jean Grey and Wolverine are in his direct line of sight. Despite this, it isn't until he takes several steps into the room that he realises they aren't his shuttle crew. (00:08:35)
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.
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