'Til Death Do Us Part: Part 1 - S2-E1
Other mistake: When Wolverine, Gambit and Beast are battling members of the Friends of Humanity, Wolverine slices through the gun of one of their members. From the angle Wolverine is standing respective to the F.O.H. member, he could not have possibly sliced through the gun without also slicing off the man's left hand. (00:12:00)
'Til Death Do Us Part: Part 1 - S2-E1
Plot hole: The establishing shot of the White House indicates that President Kelly's press conference is taking place there. A member of the Friends of Humanity disguised as a mutant busts into the room and starts terrorizing the reporters and destroying everything. The Secret Service would have either detained or shot this man long before he could have even gotten close to the press conference. Graydon Creed also shoves a security guard that tries to intervene but somehow isn't arrested for it. (00:05:50 - 00:06:35)
Continuity mistake: The exploding playing card that Gambit uses to destroy a few Sentinels and draw the rest above ground is cleverly shown to be the ace of spades (also known as the death card in some folklore), but the card he is shown charging up before the Sentinels see it is the 2 of diamonds. (00:12:10)
Continuity mistake: When Gyrich is in the car trying to get Trask on the phone, he is shown to be sitting in the backseat on the passenger side (note the windows immediately to his right and behind him). When his driver crashes the car into a tree, Gyrich is shown exiting the car from the front passenger seat. (00:08:00)
Continuity mistake: When Wolverine is searching for Sabretooth and the captive Inuits, his arms suddenly turn yellow. (00:15:50)
Night of the Sentinels: Part 1 - S1-E1
Plot hole: Wolverine bails out on the mission to destroy the files at the Mutant Registration Center to instead go look for Jubilee after she goes missing. When the rest of the team arrives, Wolverine is already there waiting for them. They flew to the Mutant Registration Center in a jet and their mission briefing heavily implied that they needed to leave immediately, so there is no way Wolverine could have arrived before them if he was off looking for Jubilee first.
The Unstoppable Juggernaut - S1-E8
Plot hole: After Wolverine deduces that Colossus wasn't the person who destroyed the X-mansion and Colossus walks away, Jubilee gets a phone call from Rogue literally less than 30 seconds later informing them that the bank was being robbed by somebody big who is later revealed to be the Juggernaut. Wolverine (now wearing a different set of clothes) and Jubilee are then shown arriving at the bank in Wolverine's jeep just in time to see Colossus being arrested for the crime while claiming he was only trying to open an account and stop the robber. If the robbery was being committed while Colossus was fighting Wolverine, then the police and bank employees would have known Colossus was not the perpetrator, not to mention the bank would have been closed off to the public, effectively preventing Colossus from going in to open an account in the first place. The only way Colossus could have feasibly been implicated would be if he was at the bank the same time that Rogue called Jubilee, which he obviously could not have reached the bank in that amount of time since Wolverine had to drive there.
Continuity mistake: When the three horsemen are climbing onto their mechanical horses, Famine's horse is in the middle, and Pestilence's horse is on the right. Once all three have all been individually shown to be mounting their horses, Famine and Pestilence have swapped places. (00:06:08)
Continuity mistake: When Gambit is saying "Someone may be tracking us," the snaps on both shoulders of his jacket are colored blue, when they should be the same brown color as the rest of his jacket. (00:11:45)
Factual error: After Wolverine falls into the ocean, he surfaces and grabs onto a platform of ice just after Sabretooth gloats about defeating him. Since Wolverine's skeleton is coated with a heavy metal, he wouldn't be able to surface. He would sink to the bottom and at the least have to resort walking to the nearby cliff wall and using his claws to scale it until he is back on the ground. (00:03:48 - 00:04:24)
Plot hole: This episode establishes that Magneto lost his family in the Holocaust, which is taken from the comics. However, the season 1 episode Enter Magneto established that Magneto lost his family when a guerilla army occupied his country.
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.
Plot hole: After Beast and Dr. Bohlson leave Carly's room, they briefly chat in the hallway just outside the door for less than 15 seconds in real time, and then discover that in that brief time frame, the Friends of Humanity abducted Carly from her second-story room via the window, managed to incapacitate the nurse, security guard and Carly's father, toss around furniture and spray paint "For Humanity" on one of the walls, all without any of the victims making a sound or the Friends of Humanity making a sound themselves. The Friends of Humanity aren't ninjas, rather they are shown to be somewhat bumbling, so there's no way they could have done all that as quickly and quietly as shown. (00:12:30)
Continuity mistake: When Archangel is lamenting his actions, the communicator devices from Storm's uniform are missing. (00:20:15)
Continuity mistake: When Gambit first walks into Bobby's cell, Bobby is sitting in a chair up against the back wall. A few shots later, Bobby is sitting in the center of the cell. (00:09:55)
Family Ties - S4-E17
Revealing mistake: When Quicksilver is fidgeting inside his containment shell, the animators neglected to properly sync his body movement. You can see that his shoulders are not "connected" to his arms, as if his head and shoulders were separated from the rest of his body. (00:16:00)
Beyond Good and Evil: Part 4 - S4-E11
Continuity mistake: The end of the episode shows Xavier standing with no assistance. The only time in the series that the use of his legs were restored were a side effect of him losing his powers. He has his powers in this scene, so there's not really any reason for him to suddenly have the use of his legs back. (00:19:15)
Beyond Good and Evil: Part 3 - S4-E10
Continuity mistake: When the Four Horsemen are retreating back into the pyramid, the opening is shown to be illuminated. When they are shown entering the opening, it is in darkness. (00:17:15)
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.
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