Goofs

(at around 1h 14 mins) When Rika's in the shower, she has a lot of shampoo in her hair. Yet right before Kayako's hand appears, the shampoo vanishes.

It is daytime when Mariko calls Rika and tells her that she's at the Saeki house. However, when Rika arrives at the house to meet up with her, it is suddenly nighttime.

(at around 1h 18 mins) When Rika wakes up in bed to a room full of yowling black cats, several of the cats are obviously statues. Some of them are even clearly replicas of the same statue.

Misaki Ito clearly pulls herself into the covers before her character is grabbed by Kayako under the bed sheet covers and dragged away.

Mariko finds it strange that Toshio has not shown up for any of his classes and it drives her to go to his address to find him. Her segment happens 5 years after Toshio was declared missing by the police, so it means that the school either never removed Toshio from their registry even after he disappeared for some reason, or Kayako and Takeo somehow re-enrolled him for classes from beyond the grave.

The Saeki house is now a crime scene after the bodies of Sachie, Katsuya, and Kazumi were discovered inside of it. Despite this, Mariko tells Rika over the phone that she entered the house to look for the delinquent Toshio that hasn't been showing up for classes, and doesn't make any mention of the house having been closed up and surrounded by police tape which would have definitely been odd to her if all she was doing was looking for a child who's skipping classes.

The curse spreads like a virus as established by the film series. Anybody who enters the house is now cursed, and so is anybody who meets that person, and someone who met that person, and so on and so forth. Although Miyuki never entered the house, she is friends with Izumi who did enter the house and even unintentionally got her friends killed as a result by making them go inside with her. Miyuki should not have survived the events of the film if going by the rules that are established.