9 Harry Potter plot holes that still keep us up at night

When Draco Malfoy disarms Dumbledore, he gains the allegiance of the Elder Wand. When Harry disarms Draco, the Slytherin is holding a totally different wand, and yet Harry becomes the master of the Elder Wand. Huh? Isn't it supposed to be the wand that you disarm, rather than any wand they own?

Ollivander must be very, very nice, or very, very in debt, because fans have been questioning for years how he sells his wands so cheaply.

In the Wizarding World, a unicorn hair costs 10 galleons, while a wand containing unicorn hair, phoenix feathers and Hornbeam, for example, from Ollivander's will only cost you seven galleons. What?

We hear about The Dark Lord and Severus Snape's experience of Hogwarts, but what about the rest of the Death Eaters? Did Bellatrix Le Strange go to Hogwarts, or were they schooled in Witchcraft and Wizardry elsewhere? Because presumably if it was Hogwarts, they know the likes of Molly Weasley, and Dumbledore? Why is this never mentioned?

In The Order of the Phoenix, Sirius Black reveals Peter Pettigrew's secret and is able to prove his innocence in one sense, but isn't able to clear his name to the wider wizarding world. So when he's sent to Grimmauld Place, he breaks his rules of confinement to see Harry in his anigamus form and is told by the Ministry that he's close to being sent back to Azkaban. Why doesn't he just make some Polyjuice potion, which, as Harry, Ron and Hermione prove, is capable of fooling even the most senior of wizards, instead?

When Harry, Ron and Hermione take Polyjuice potion to gain access to Bellatrix's vault in Gringotts during Deathly Hallows, they don't adopt the same voices as the people they're impersonating, and Hermione has to try and put one on.
Does that mean Barty Crouch had to perfect Mad Eye Moody's voice and use it for a whole year? Surely Dumbledore would've picked up on this? Had he perfected it THAT much?

A questionable flaw in Philosopher's Stone lies in what fans are dubbing 'the missing day' between when Hagrid picks Harry up from Godric's Hollow, and when he drops him off with Dumbledore and Miss McGonagall at 4 Privet Drive.

Voldemort kills Harry's parents on November 31, and though Hagrid rescues Harry from the ruins of the house that evening, he doesn't arrive at the Dursley house until gone 11pm on 1 November - despite insisting Sirius Black’s magical flying motorcycle made his journey very easy.

One of the most confusing bits about Harry Potter is how long travelling somewhere seems to take. While the train to Hogwarts from Platform 9 3/4 takes a whole day, Harry, Ron and Hermione make it to Gringotts in London much, much quicker. Oh, and apparating takes a matter of seconds, driving a flying car is comparable to the train and broomsticks even quicker. Hmm.