Death on the Nile?
At the end of the movie, Poirot is called away to Egypt because there's been a murder on the Nile. Obviously an allusion to the novel 'Death on the Nile', and perhaps setting up the next movie if this one is successful.
Problem is, Poirot was present for the murder on the Nile, and it would be a much different story if he was called in on the case. Not a big deal, just pointing out an interesting issue. And it would make things a little awkward if they actually do decide to make Death on the Nile next.