When Nyles is giving the chocolate bar analogy, first he has a partial bar he has taken a bite of, but when the shot returns to him, he has a whole bar.
The length of Nyles's right blue T-shirt sleeve between shots when he is asking Sarah's step mother about her room.
When in the pool at the end of the movie, talking about Nyles's dog, Sarah's head is up then back on the inflatable in the next shot at 1:22'45".
During a recreational shooting on Spuds' estate, Sarah and Niles shoot a photo of a man with a mustache. When Sarah asks Spuds, "Hey, who's the mustache?", Spuds replies, "Prick my wife run off with." In the very next scene, Sarah pumps a rifle and smashes the head of the man with a mustache. In that scene, it is clearly visible that the photo was blown from the back, and not from the front.
When Sarah wakes up Nyles is already in the pool with his friend Jerry, which makes it impossible for Sarah to sneak out to study when Nyles tries to find her every morning. However, Nyles could never find her because she never woke up in her own room, and it would be easy to sneak out undetected without going by the pool.
When Sarah hits Roy with the police car, Roy wears a dark mustache inconsistent with the natural gray/orange scruffy beard he had in every other scene. This is because Roy has disguised himself to sneak up on Nyles, shaving the beard and adding the fake mustache. His look resets to normal the "next" day.
The first depiction of his earthquake clearly shows that the camera is shaking but neither the goat or the vegetation behind it.
When Sarah's dad and step mom are about to sing (about 3/4 of the way into the movie), the people sitting behind Nyles start swaying to the music before the couple finishes speaking.
Roy states that the nurse would not let him go to sleep to make sure he would not fall into a coma. Either a patient is stable enough and can safely sleep and his vitals will be monitored, or he is not stable (probably Roy's case) and the ICU or emergency doctor will actually want to put him in an "artificial coma" (i.e. medically induced coma) to enable them to monitor and treat the patient better (common Hollywood mistake called the "stay with me!" or "stay away from the light!" magical medication).
When Sarah starts throwing beer cans at Nyles at the pool and he falls in, his sunglasses come off (and you clearly see him not wearing them), but when Sarah jumps in you can see him wearing them, and when they come up out of the water he isn't wearing them again.
As Sarah is drinking from her "Go Bold" cup (near 22:18), she puts the bottom lip of the cup on her chin, not on her lip, like normal people drink.
The goat experiment and the mid-credits scene are contradictory, since Sarah said the goat vanished completely from the time loop, but after Sarah and Nyles blow themselves up, Nyles reappears in Roy's time loop when Roy approaches him at the wedding.
Toward the end of the movie when Nyles says "dot, dot, dot" in his speech. Sarah corrects him and says, "it's called an ellipses." 'Ellipses' is the plural form of ellipsis. 'Ellipsis' is the singular noun describing a punctuation mark represented
by three dots.