Niosi's voice credit was removed from Fire Emblem Heroes, in which he voiced Byleth. Soon after that, we saw that Byleth was being voiced by a new actor in the most recent trailer. This whole situation started on Tuesday of this week, and now we have a comment from Nintendo of America on the matter.
“After assessing the situation, we decided to re-record the character’s voiceovers in Fire Emblem: Three Houses and Fire Emblem Heroes with another actor. The new voiceovers will be included in a future patch.”
As many fans suspected, Nintendo is going to remove/replace Niosi in Fire Emblem: Three Houses as well. We'll be sure to let you know when the patch is released.