When Tree shoots Tombs, she fires only three rounds before the slide is shown locked back. This indicates that the magazine is empty at that point. This pistol carries more than a dozen rounds in the magazine. No officer would ever carry only three rounds in their magazine, the magazine would be full.
When Tree tries to fire the officer's pistol she is told by Tombs, "The safety is on". Tree had just removed the weapon from the officer's holster. Almost no police officer carries his sidearm with the safety on, they are always carried with the safety off.
When Tree tells Gregory that she knows about his wife and sets him free, it makes no sense for Gregory to threaten Tree with not letting her pass his class, as Tree could simply blackmail Gregory with telling her wife about their love affair.
When Tree escapes the hospital room, she has slippers on. After she sneaks by the nurse's station and enters Gregory's office, she is no longer wearing slippers, but in the next scene with Gregory and the killer, she's wearing slippers again.
During the night that Tree locks herself in her room, she approaches the TV and the clock shows the time as 9:24. The camera changes angles, and when it shows the same shot again - it now shows 9:31. It changes shots and returns once more and shows 9:24 again.
In the second day, during the lunch meeting, Carter once again spills chocolate milk on Tree. The position and amount of chocolate milk spilled across her shirt changes position and amount between shots.
Around 1:09, in the hospital parking garage, when Tree is about to escape using the car, she pulls the gear shift back and smashes into the car behind her. Now, we see the gear shift in forward position, again, before she pulls it back, again, and drives away.
After Tree and Danielle are accidentally run over by a bus, Tree removes her from the suspect list. Since the bus driver was clearly not the murderer, it did not prove that Danielle is not the murderer.
When Tree is in her hospital room, there is a rack by the door containing three boxes of latex gloves, all size (S)mall. A real hospital room always stocks three different sizes of gloves: (S)mall, (M)edium and (L)arge, because one size of gloves does not fit all hands.
When Tree is attempting to elude the masked killer in the hospital parking garage, she flees in Gregory's silver Mercedes-Benz, using a floor mounted shifter, which that model does not have. In the US all Mercedes-Benz models come standard with a steering column mounted shifter.
Carter tells Tree that she passed out at the party, and he brought her to his room because he was afraid that she might fall or choke on her own vomit like Janis Joplin. Janis Joplin's cause of death was taking a heroin-alcohol overdose.
When the police car is side swiped, the black charger shows no damage to driver side at all. It should have scrapes or broken mirror. As the fire starts in crown victoria, the gas is bubbling up around fuel door gas wont bubble up and there would be gas cap in way if it could. The gas would have to come from behind body panel, but damage was not enough for that.
It doesn't seem to matter how soon Tree decides to leave the dorm room after waking up. Even when she rushes out of the room, Carter's roommate shows up right away without any regard to the original conversation . The environmental girl still walks up to her at the same time the sprinklers go off at the same time, the frat guy falls down at the same time, etc. In case Tree leaves the dorm so quickly, she should be ahead of all of these events.
During the last day from the loop, how could Tree have the time to get close and so friendly with Carter, after leaving so quickly in the morning? Isn't she supposed to spend time with the police for interrogation or/and probably get arrested for murder charge against her roommate Lori, until the situation is clarified and she is exonerated? Instead, she is free like if nothing was happened.
At one point, Tree plots out a way to kill Tombs. She goes to the hospital, pulls a knife on the officer, takes his gun, tells him that Tombs is about to escape and to go get help. She then goes into his room where he escapes, they fight and she shoots and kills him. She's then seen celebrating her birthday. There is no way that she'd be free that night - she would at the very least be charged with the murder of Tombs since there's no witnesses to see that he did in fact free himself. From an outsiders point of view, she took an officers gun, untied Tombs, and then killed him.
When Tree begins to investigate each day and follow one person to see if they're the killer, she keeps making a list. When the list is shown on subsequent days, we see the other names already crossed out. This list needs to be made every new day. Why would Tree keep making a list and cross off names again? She simply wouldn't put those names on any more lists. The scribbles marking off names are the same indicating that it's the same piece of paper, which is not possible.
When Tree is at the hospital and Dr. Butler is giving her a physical checkup, he tells her that her injuries that were accumulated from her numerous deaths prior mean that she should already be dead. Tree deduces that this mean that the time loop won't be infinite and that she will eventually permanently die. This is a plot point that although is relevant in the alternate ending, where Dr. Butler's wife pretends to give Tree medicine for said injuries before killing her, it is never addressed again and forgotten in the theatrical cut, a result of bad editing.