Family Ties - S4-E17
Other mistake: This series is in the same continuity as the other Marvel animated series that aired around the same time - Spider-Man, Iron Man, The Incredible Hulk, and Fantastic Four - by virtue of each aforementioned show crossing over with at least one of the other shows. However, in Iron Man, Scarlet Witch has an Eastern European accent, and in this episode she has an American accent.
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