One thing that didn't make a whole lot of sense...
..in the movie compared to the book.
The whole thing about the clues leading to the virus makes more sense in the book than in the movie. In the book, Zobrist sets up the treasure hunt (so to speak) because he wants the world to know the location where the virus was released – he has a plaque made to commemorate what he figures will be a turning point in human history, and he wants to be remembered, as well.
In the movie, the purpose of the treasure hunt is for Sienna to find the virus and release it – but it makes little sense that he would leave something that was so important to him (“saving” humanity by killing half of it) up to chance. What if she couldn’t find it, or if others found it before her (which is exactly what ended up happening?). Then all his work would have been in vain, and for what? Just to satisfy his girlfriend’s taste for games?
Don't give me songs
Give me something to sing about