Fear Comes in Waves
Why it is hard sci-fi
A small group on a yacht is caught in a storm and boards a derelict cruise liner that turns out to be a closed temporal loop. The film commits to the rule. The protagonist is caught in a cycle that resets every time it ends, and her own past selves are also on the ship. The film is rigorous about who is on which loop and what each one knows.
Science inside it
Closed temporal loops with multiple instances of the same person co-existing, deterministic reset on a fixed trigger, and the operational shape of a Sisyphean myth structure played out on a finite stage. The films rule is Mobius-strip-shaped rather than branching, and it commits to that geometry.
Spoiler alert
The protagonist is being punished for her sons death in a car accident at the start of the film, and the loop returns her to that moment every cycle. The film closes the loop visibly, with each cycle ending where it began, and the protagonist accepting the role.