The film is set during summer vacation, yet the texts Sarah receives throughout the movie say the month is October.
When Sarah is sneaking through the cornfield at the Tod house, she trips over a large rock that nearly gets her impaled on a piece of machinery. A rock that big would have been found and removed from the field prior to plowing it and planting the corn, because it could break the machinery if it gets hit.
When Sarah (Anna Kendrick) is in the bus, she finds Jillian's phone, and it is on. Jillian had been gone for a couple of weeks at that point, and her phone shouldn't have needed to be recharged.
A minute later she finds the phone of Janet, who had been missing for years. And still, her phone works perfectly fine, and it even has enough power to make a call.