Continuity mistake: When Xavier helps Morph overcome Mr. Sinister's mind control, Wolverine, Storm, and Gambit are standing behind Morph, and Magneto is lying on the ground. When the shot changes, Storm, Gambit, and Magneto have disappeared. (00:18:35)
Other mistake: When Gambit is consoling Rogue just before she is taken to be tortured, he tells her that he loves her, and states that he has never said that to anyone before. But as we learned earlier in the season, Gambit was engaged in his youth to Bella Donna. Surely he told her he loved her at some point. Rogue is aware of this aspect of Gambit's past, so he would have nothing to gain by lying to her about it.
Continuity mistake: When the X-Men regain their mutant powers, Jean Grey is suddenly wearing her uniform instead of the casual outfit she was wearing when she was abducted. In the next shot and for the remainder of the episode, she is back to wearing her casual outfit.
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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