Plot hole: The innocent who gets Piper's powers uses them to freeze Piper and Phoebe. But even though Piper and Phoebe no longer have their unique powers, they are still good witches; they were still able to scry, and we have encountered good witches on the show in the past who had no powers at all. And by the rules of magic within the show, good witches do not freeze.
Plot hole: When Paige and Leo are talking in Leo's office at magic school, Paige compliments Leo for being such a good headmaster. She mentions that after being headmistress for a year, it's harder than it looks. If she became headmistress after they killed Gideon (i.e. when baby Chris is born) and she's been headmistress for a year, that would make Chris at least a year old. Chris is obviously not one year old just yet.
Plot hole: When Grams is summoned for Chris's wiccaning, she reminds Piper of "the talk" they had when she was a teenager, about how important and special being a witch was to Grams and how it would be to the girls someday. But in the first episode, the girls have no inkling they are witches, and when they find out it's passed through the maternal line, they wonder if Patty or Grams was a watch-suggesting that they aren't sure or have no memories of them as witches. I know there was some memory altering at certain points, but why would Grams have a conversation specifically about how great it is to be a witch and then erase that?
Plot hole: When Leo tells Piper that he believes he found the demon Sargon in the Book of Shadows (which may be the demon Count Roget made a faustian deal with), Piper looks at it and says that they vanquished this demon five years ago. Which would've meant they vanquished the demon with Prue. When in fact the only demon that happened with was Zahn in season 6 episode 6, "Soul Survivor," and they did that with Paige.
New this month Plot hole: The sisters are preparing for a big showdown with Zankou and vaguely discussing their plan. They don't outright say it (so as not to give it away) but discuss how they wished they "had learned it sooner" but "Prue was very protective of it." They're discussing astral projection which originally was stated as a Prue-specific power and not one that could be taught. The show ignored the original introduction of the power as developing naturally as one of Prue's powers, and was not an ability that could be learned, just so the episode had a way for the sisters to defeat Zankou.
Plot hole: When the man and woman receive Piper and Phoebe's powers, the lady freezes the man and Phoebe due to fear, but good witches don't freeze, so if Phoebe froze (which she shouldn't have due to only her active powers lost) then why did the man? If he had Phoebe's powers then he isn't mortal and therefore should not freeze.