Audio problem: When Lionel tells the others to lift the button at the center of the compass, you can notice that the music box is still playing, but the drum of the machine is still. (00:08:30)
Audio problem: When the country music singer tells Parker that Elvis can sing his songs "but no wiggle" there's a side shot of his face and his mouth doesn't match what he's saying.
Audio problem: Near the beginning of the film, when the sheriffs are chasing Kya, she takes her boat through some trees. The main sheriff says "in there," or something similar. His mouth doesn't match what he is saying.
Audio problem: Katherine visits Poirot at the field hospital; the opening line has a loud gulping, most likely dubbed, and then Branagh's voice says "I asked you...not to come" with the second part of the sentence added in dub; his lips don't move. (00:05:45)
Audio problem: When the boy and the leader of Iceland are hammering in posts and the boy is complaining that he's the heir and shouldn't have to do manual labor, there are at least two times when bad wind flutter in the microphones can be heard. It sounds like the wind clips the volume level and the audio briefly cuts out. It happens on windy film shoots, as wind screens can only prevent so much and its obviously very windy in this scene. Why this wasn't caught in post is hard to say. This is audible on the video on demand version.
Suggested correction: No such problem exists on the UHD/Blu-ray release. I also did not notice it on the VOD release, so it could have just been an issue with your sound setup.