No Mutant Is an Island - S5-E4
Revealing mistake: When Killgrave is saying "On your knees," his eyes jump off his face. (00:18:45)
No Mutant Is an Island - S5-E4
Revealing mistake: When Rusty is being brainwashed, his eyes move down his cheeks as his head nods. (00:10:55)
No Mutant Is an Island - S5-E4
Revealing mistake: When Sarah turns off the stove burner you can see that there is an outline of a knob that the animators either forgot to fill in or forgot to erase. (00:05:35)
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.
BaconIsMyBFF