It could be (https://tvtropes.org/pmwiki/pmwiki.php/ExecutiveMeddling/LiveActionFilms) changes to the script, the firing of actors, or completely changing the ending due to focus groups.

Ridley Scott's Legend (1985) is an extreme example of studio execs going crazy with changes after test audience screenings. The version released in Europe is closer to the director's original vision. The US version has almost an entire hour cut out of it, with a new score and many changed sequences. It's basically a different film, as mentioned in several YouTube videos (https://www.youtube.com/watch?v=1M7N_TSZdic). The characters change, their motivations change, and the mood changes. The European version feels like a Disney musical; the US version feels almost like a horror flick. I've never seen such a change in tone between two edits of a film.