'Harry Potter' Loose Threads We Probably Shouldn't Pull

The books mention that Azkaban prisoners have their wands confiscated, and some wands are even snapped to avoid the possibility of the witch or wizard using them again.

According to this practice, Bellatrix Lestrange and her cohorts shouldn't have their original wands after they escape from Azkaban, but they do. It's confirmed that Bellatrix is using her own wand because Ollivander mentions it's the same one he sold to her when she was 11. 

If Hagrid's wand was snapped when he was expelled from Hogwarts as a student, why didn't the Death Eaters' wands get the same treatment?

Harry receives the Marauder's Map from Fred and George in his third year and quickly spots Peter Pettigrew's name. Pettigrew is under his Scabbers Animagus disguise at the time, yet the map still shows his true identity.

Why Fred and George fail to see Pettigrew on the map is a mystery, because they've been around him for five years at Hogwarts. Scabbers originally belonged to Percy, and the twins are at Hogwarts for two years with Percy before Harry and Ron become students.

So either Fred and George saw a mysterious man named Peter Pettigrew for years and didn't tell anyone about it, or this plot thread just didn't cross the author's mind.

Lily and James Potter use Peter Pettigrew as their Secret Keeper, a decision that backfires horribly when he sells them out to Voldemort. None of this would have been an issue if the pair had just been each other's Secret Keeper.

The arrangement follows the Secret Keeper rules because one person would have to reveal their house's location, and either of them could do so. 

James and Lily weren't expected to leave the house at any time, so nobody was in a position to find them.

Nearly Headless Nick is petrified when the basilisk stares right through him at Justin Finch-Fletchley. Nick doesn't perish because he's already a ghost, so the most that happens is he's left in a catatonic state.

The ghost returns to his normal state after the Mandrake potion is prepared, but this shouldn't be possible because Nick can't drink anything: He's transparent and incorporeal.

It's never explained how the ghost is revived, or even why he would become petrified; he doesn't have any organs that should be affected by the basilisk's stare.

Harry Potter readers and moviegoers follow the protagonist's point of view during the Triwizard Tournament, which ensures they are part of the action. When it comes to the perspective of the audience, though, the tournament is mostly missing any action.

The First Task, with the dragons, is the only one where spectators see anything; they are completely in the dark during the next two. 

Nobody knows what happens underwater when Harry tries to rescue all the captives; instead, the merpeople have to relay this information. Likewise, the Third Task is obstructed by giant hedges, so no one can see Harry and Cedric transported to Voldemort.

Barty Crouch Jr. and Voldemort's scheme would have been up in flames had the tasks been available to view. It's laughable that a tournament intended to entertain couldn't even be seen by anyone. 

The Fantastic Beasts series reveals that the International Confederation of Wizards is the equivalent to the United Nations in the Muggle world but carries far more authority.

When the situation around Gellert Grindelwald escalates, the ICW intervenes and sends Aurors to apprehend him. 

The ICW works in tandem with MACUSA (the Magical Congress of the United States of America) and the British Ministry of Magic, so why doesn't the confederation step in when Voldemort becomes a big threat?

Voldemort is considered more evil than Grindelwald, so it would make sense for the ICW to send in far more Aurors to combat him. But the opposite happens, because Britain is left to its own devices and the ICW is silent during both the Wizarding Wars.