Fantastic Beasts: The Crimes of Grindelwald is a sore subject amongst Harry Potter fans. The film suffers from a glut of characters, the story is bloated, and it messes with Harry Potter universe canon.
Crimes of Grindelwald issues range from fandom-shattering inaccuracies like the age of Professor McGonagall to smaller things like what specific spells actually do. Unfortunately, there’s no one to blame for the Fantastic Beasts retconning issues other than JK Rowling.
The author’s held a tight grip on her content, which has lead her to smooth out and “fix” problems with her original story. Unfortunately, there’s decades of established lore, which makes the changes in Fantastic Beasts feel akin to George Lucas’s attempt to change the Star Wars universe with his prequel trilogy.
Some of Crimes of Grindelwald’s retcons really do muddy up the narrative of the Harry Potter films, but a few of the odd plot holes could turn out to be red herrings by the end of the Fantastic Beasts series. Unfortunately, we only have two movies to judge in 2018. And as it stands, canon-breaking retcons are a huge problem.
In Potter-lore, it’s well established that Professor McGonagall was born in 1935, and she took a job at Hogwarts in 1956 after working in the Department of Magical Law Enforcement at the Ministry of Magic for two years. Even though Rowling wrote the literal book on McGonagall, she changed the professor’s timeline and created a major plot hole in the lore.
Retconning McGonagall's timeline doesn’t do anything for the narrative of Crimes of Grindelwald, but it does make her an Easter egg for a particular group of fans who aren’t concerned about things like plot or the well-established timeline of the Harry Potter films.
That said, some fans are doing mental gymnastics to help the character’s appearance make sense. According to this group, Minerva McGonagall's grandmother was also named Minerva, so the character in the film could be the grandmother rather than the character fans know.
In the final moments of Crimes of Grindelwald it’s revealed Credence Barebone is actually Aurelius Dumbledore - Albus Dumbledore’s long-lost brother. That’s a huge twist, but it creates a problem with the canon. According to Rowling, Credence was 18 in 1927, when means he was born in 1909. That doesn’t jive with Dumbledore’s backstory.
According to series canon, Dumbledore’s father Percival was incarcerated in Azkaban after attacking a group of muggles who were assaulting his daughter. He died in prison in 1890. His wife, Kendra Dumbledore, died nine years later. Grindelwald could be lying to Credence, but it’s safe to assume he’s not.
As far as plot holes go this isn’t Earth-shattering, but it’s still a weird mix up of facts. In Crimes of Grindelwald Dumbledore teaches Defense Against the Dark Arts. While he looks like a fun teacher, it’s well established that Dumbledore spent his time at Hogwarts teaching Transfiguration (the art of changing the form and appearance of an object or a person) before becoming headmaster.
According to Half-Blood Prince, Galatea Merrythought taught Defense of the Dark Arts for at least 50 years prior to Tom Riddle graduating from Hogwarts in 1945. So for all intents and purposes she should be teaching DODA in Crimes of Grindelwald and not Dumbledore. If you have a splitting headache right now you’re not alone.
In the finale of Crimes of Grindelwald, Leta LeStrange dies at the hand of the dark wizard baddie which puts an end to her family line. The problem this creates is there’s now no one to sire Rodolphous LeStrange.
The only reason Rodolphous is important is he marries Bellatrix Black, giving the wizarding world its most intense villain with the coolest name. Unless Leta’s death was fake, another LeStrange (hopefully also named Corvus) needs to show up ASAP to make any sense of this.