'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: Professor X's wedding tuxedo suddenly changes into his usual green suit when Beast is giving an update about President Kelly. (00:05:50)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: The ribbon on the wedding present that Beast is carrying disappears when Jean's bouquet lands on it. (00:05:30)
Continuity mistake: When Magneto is battling the Sentinels after they have rescued Senator Kelly, bandages suddenly appear on Magneto's right arm, something that's not supposed to be there until after the X-Men have rescued Magneto and patched him up. (00:04:25)
Continuity mistake: Magneto reveals to Senator Kelly that he went to Washington, DC to personally witness his assassination. The flashback to the previous episode reveals that Magneto was watching Mystique (masquerading as Gambit) attempt to assassinate Kelly and the real Gambit's intervention through a window. Magneto can be seen as plain as day watching in the window in the flashback, yet in the actual episode, Magneto is never there. The design of the window is also different, as well as the color of the curtains. The room itself also appears to be smaller in the flashback.
Days of Future Past: Part 2 - S1-E12
Continuity mistake: When Rogue punches the Blob, her arm is shown to be sinking into the middle of his chest. When the shot changes, her arm is suddenly in his stomach. (00:12:25)
Days of Future Past: Part 1 - S1-E11
Continuity mistake: When Wolverine is telling Bishop that he's not letting him out of his sight, the tubes on the back of his right hand are missing, and then are there in the next shot. (00:17:20)
Continuity mistake: The stains from the tomatoes that are thrown at Beast disappear from his jumpsuit. (00:10:05 - 00:10:55)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Rogue goes to touch Wolverine with her bare hand to stop him, she is shown removing the glove from her right hand. After Wolverine collapses, Rogue is now missing the glove from her left hand, and her entire left arm, including the hand, is solid green. (00:11:55)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Rogue catches the security guard from the collapsing tower, he has black hair. When she is flying through the air with him as well as when she dumps him in the grass, his hair is red-orange. (00:06:50)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Gambit says "You wanna play with Gambit? Here, take a card!" the glove on his right hand is missing, then is suddenly back on his hand when he says "House wins." (00:05:50)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: The position of the police cars around Sabretooth change from shot to shot. (00:01:15)
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