In this episode it is established that Paige was born in 1975, which would make her the same age as Phoebe. This is incorrect, because in episode #4.2 "Charmed Again, Part II", she says her date of birth is August 2, 1977.
When Paige is explaining to Phoebe about how she is her sister in the Manor kitchen, the close ups of Phoebe show she only has one earring in. In the distant shots when Darryl is behind Paige, You can clearly see Phoebe now has both earrings in.
When Piper rushes Paige into the back hall because she is about to sneeze, look at where the door is hinged. The door is hinged so that it swings in, and the door handle is to the right of the camera. In the next shot, when Paige goes to exit the back hall, the door handle is now on the left side of the door, and opens outward.
Paige's birth date is wrong on her tombstone.
The potion to vanquish Cole made by Prue & Piper in Season 3 was purple in color, yet when Paige, Piper & Leo make it this time it looks to be orange or yellow. If made with the same ingredients, it should be the same color.
When Leo shows Paige her gravestone, she deduces that that her powers are gone because she never received them by reconstituting the power of three. This however is false, seeing as originally Paige had her Whitelighter abilities for her entire life and showed so when she Orbed away from Shax. Her Orbing is not tied to her Charmed powers so technically she still should have had them in Cole's alternate reality.
While in the cemetery, Paige observes that all the demons that she and her sisters vanquished in "the real world" are still alive in that world. However, one of the demons, Darla (aka. Sucubus) was vanquished by the Charmed Ones prior to Paige arriving on the scene and since she was vanquished by Prue, Piper and Phoebe, Darla should not have been there.