Time travel movies can quickly become complex; amid all the timelines, future and past selves, and toing and froing, some sci-fi movies even break their own rules. The concept of time travel has a long cinematic history and any film that employs the high-concept plot device must negotiate the hypothetical physics and establish its own time travel lore. Choosing between single and multiple timelines and whether time travelers can change the past or not is no mean feat, not to mention maintaining theoretical consistency and heeding to established rules across an entire movie and sometimes even sequels.

https://screenrant.com/sci-fi-movies-time-travel-fail-mistakes/