Yeah, at first. Almost every show has it take a bit for the VA's to grow into their characters. After a certain point in TLA, I would not agree that it was an issue. They truly delivered on the emotionality by the time it was necessary to give important lines. On the other hand, this is the 3rd year of Korra's existence, so it's odd that the VA's still sound as flat as they do.
I can't think of any voice work that felt jarring to me other than General Iroh's and Zaheer at first (the grey mane threw me off completely).