I've personally noticed brows and/or lips twitching on several faces while using emotes/expressions: ♀ Elezen Face 4; ♀ Highlander Face 1; ♀ Midlander Face 2; ♂ Midlander Face 4; ♀ Au Ra Face 2; ♀ Au Ra Face 3; ♂ Au Ra Face 3; ♀ Roegadyn Face 4; ♂ Lalafell Face 2; ♀ Viera Face 2; ♂ Viera Face 2; ♂ Miqo'te Face 1; ♂ Miqo'te Face 4.

At the very least, on ♀ Elezen Face 4 the issue seems to be exclusively eyebrows for only a couple of emotes, while on faces like ♂ Viera Face 2, nearly every single expression has twitchy lips and eyebrows. Regardless, I think it's safe to assume this is happening to every face option in the game to some extent.