One day, someone decides to create a work of fiction which turns out to be a huge success. To cash in on its success, numerous spinoffs and licensed material might be produced that are centered on that particular work, with many of them claiming to be canon with the original work.
But then from out of nowhere, the creator decides to produce their official follow-up, which flat-out contradicts what happened in the spinoff material. Looks like the writer of that one tie-in book was too hasty with killing that seemingly unimportant character. Or they incorrectly predicted how the aftermath of the original story would turn out.
This usually happens because the creator is unaware of the spinoff material (after all, it may have faded into obscurity during the Sequel Gap) or because they have deliberately chosen to retcon the spinoff out of existence, or there was simply miscommunication between the creator and the tie-in writers.
Compare Series Continuity Error, where two or more installments of the same branch of a franchise unintentionally contradict each other. See also Early Installment Weirdness and Continuity Snarl. Often results in Characterization Marches On when a character from the original work ends up behaving differently in the followup than they are depicted in the spinoffs. Not to be confused with Schrödinger's Canon, where there's still a chance that the spin-off in question might be considered canon. The Fanon counterpart to this trope is Outdated by Canon, and for mere fan theories it's Jossed.
- The original Star Wars Expanded Universe (now known as Star Wars Legends) was loaded with decades of novels, comic books, video games, TV shows, etc. that often contradicted each other and even the movies themselves in some way. This is probably why when Disney acquired Lucasfilm in 2012, they jettisoned almost everything associated with the franchise apart from the Original Trilogy, Prequel Trilogy, and Star Wars: The Clone Wars to make way for the Sequel Trilogy and other Disney-produced material.
- A great example is the first piece of EU/Legends fiction, the novel Splinter of the Mind's Eye, which was published between A New Hope and The Empire Strikes Back. It was intended as a possible TV Movie canon sequel by Lucas in the event that A New Hope didn't pan out. Among other things; Luke and Leia are implied to have a budding romantic/sexual relationship.
- Another example was the Clone Wars. Before Attack of the Clones came out, there were several allusions to it, though Lucas himself prevented any direct mention of it. A lot of writers assumed that the clones attacked the republic, rather than fight for it.
- A lot of the filler that tried to expand on the lore of Dragon Ball Z was rendered moot the more the manga kept going. The most important one is the despiction of Saiyans as no better than cavemen, as Dragon Ball Super actually reveals they were civilized enough to wear proper clothes like battle armors made of leather.
- The anime adaptation of Saint Seiya introduced several elements that contradicted the Manga. The most noteworthy example would be Hyoga's master. The manga introduced a Canon Foreigner called the Crystal Saint as his master, only for the manga to reveal that it was actually Aquarius Camus. The Anime tried to patch this over stating the Camus was the master of Crystal Saint.
- DC Comics' Star Trek #1 was created as a direct sequel to Star Trek II: The Wrath of Khan, and takes place immediately where it left off. Unfortunately for the comic, Star Trek III: The Search for Spock would be released just a few months later, and would also directly follow up on events from Wrath of Khan.
- Any portrayal of the Space Jockeys (now known as Engineers) in the Alien, Predator, or Alien vs. Predator expanded universe prior to the release of Prometheus is guaranteed to fall under this trope.
- The Infinite Loops has a handy explanation for this: expansions and variant loops. See, the unknown disaster that caused the loops forced most of the multiverse to re-start from backups- i.e. their media in our world. Because of this, anything that isn't explicitly stated in canon varies from loop to loop (i.e. the Walled Kingdom shifted locations frequently because the canonical world map of Attack on Titan was only revealed later and is a spoiler to boot, and Gilda's backstory was usually something very different from Griffonstone). Loops sometimes get 'expansions' (i.e. continuations of the media) that can stabilize more of the loop- which, out of universe, is the writers taking new canon into account. It's usually fairly well-worked in, with stories of loopers coping with baseline deaths and the loss of what they considered their childhoods.
- Service With A Smile:
- Adam Taurus is an Adaptational Nice Guy, which was an intentional change, but it was done before Adam went completely psycho in volume 6. The author admits he probably wouldn't have bothered making him nice if he had known. Adam is also able to take off his mask and blend in, while in canon there's a large brand over his left eye.
- Adam tells Blake that no one in the White Fang really noticed when she disappeared; she wasn't particularly high-ranking, and those who remembered her just assumed she died on a mission. Canon soon revealed that not only was she a high-ranking member of Adam's White Fang, but she was the daughter of the original founder. Everyone noticed when she disappeared.
- Alien: Covenant puts the final nail in the coffin of the Alien vs. Predator films by revealing the xenomorph, as we know it, didn't exist until the events of Alien: Covenant, as they were created by David mucking about with Engineer biotech.
- Incredibles 2 is a direct sequel to The Incredibles, and ignores any other follow-ups to the latter (like the comic book series and the video game Rise of the Underminer).
- Pirates of the Caribbean: According to prequel books, Jack Sparrow used to work for the East India Trading Company, was made captain of the Wicked Wench, untill he refused to transport slaves, resulting in Cutler Beckett branding him a pirate and sinking his ship (which would later become the Black Pearl thanks to Jack's deal with Davy Jones). The movie Pirates of the Caribbean: Dead Men Tell No Tales however shows Jack becomming a pirate captain after inheriting both his magic compass and the Wicked Wench during a fierce battle against the pirate hunter Armando Salazar, and cementing his position as captain by defeating Salazar.
- The Lion King: Six New Adventures was a series of licensed book sequels based off of The Lion King. They starred Simba's son Kopa and gave info on things like Simba's grandparents and Scar's youth. Come the direct-to-video sequel The Lion King II: Simba's Pride and Kopa has been replaced with a daughter named Kiara. The series The Lion Guard also features a different backstory for Scar (and, though it acknowledges that he had a different name once, it doesn't outright call him "Taka"), though whether the cartoon is canon to the films or is in an Alternate Continuity is up for grabs.
- The Journal of the Two Sisters is a companion book for My Little Pony: Friendship Is Magic written by one of the show's writers. The canonicity of the book has been pulled into question due to inconsistencies with later episodes of the show. For example, the book states that other alicorns existed in the past and it's heavily implied Celestia and Luna were born alicorn. Season 6's "The Crystaling" implies that Flurry Heart is the first alicorn ever born in Equestria. The book's writer - who doesn't work on the show anymore - tries to handwave this as the sisters being born before Equestria. The episode "Shadow Play" also strongly counters the book by depicting the Tree of Harmony as younger than the book does.
- Older Than Steam: After Cervantes wrote Book I of Don Quixote, an unknown writer using the pseudonym of Avellaneda published a second part, wholly without Cervantess permission. This spurred him to write the proper sequel, in which Avellanedas volume exists in-universe, and causes the real Quixote to have a breakdown when he discovers it, since he knows he didnt do anything described within it.
- 007 Legends, which is a tie-in to Skyfall, features a level loosely based on the film On Her Majesty's Secret Service, where Daniel Craig's incarnation of James Bond meets and confronts Ernst Stavro Blofeld. Guess who Craig!Bond ends up meeting for the first time in the next film after Skyfall?
- Castlevania: Circle of the Moon began development as a standalone Gaiden Game separate from the series's main timeline, but as its storyline was not explicitly contradicted by the main series, it wasn't impossible for its events to have taken place after all... that is until Order of Ecclesia was released, its events occurring within a similar time period as Circle of the Moon and thus making it extremely difficult for the two to occur in the same continuity.
- Spider-Man: The New Animated Series, which was an animated follow-up to the first Sam Raimi Spider-Man film, depicts Dr. Curt Connors becoming The Lizard, and then seemingly falling to his death. These are never brought up in Spider-Man 2 or Spider-Man 3, which came out after the series finished its run and feature Dr. Connors alive and well.