I was writing a ranty post about the "splitting" and "lumping" I tend to see in the fandom -- "lumping" being combining all characters from every bit of TLK media into one single "universe" rather than treating them as existing in separate continuities; while "splitting" is treating a single character as two or more different individuals.
When I started working on a paragraph mentioning how the various inconsistencies in the numerous TLK tie-in material makes it virtually impossible to cram every aspect of the TLK universe into one single continuity without some arbitrary picking and choosing, that paragraph ended up so long that I decided to just make a thread dedicated to inconsistencies instead.
Timon:
The Lion King 1 1/2: When hyenas invade his colony while Timon is on guard duty, Timon decides to leave his colony in the hopes of finding a place where he can fit in.
"All Mud and Motor Mouth" (The Lion King: A Nature Fun and Learn Series): While he is on guard duty, Timon starts reporting every single thing he sees to the rest of the colony, no matter how harmless or insignificant. Thus, when real danger appears in the form of an eagle, no one responds to Timon's calls for help, and the meerkats are lucky to escape the eagle's attack. When Timon is blamed for what happened, he decides to leave his colony.
"Hakuna Matata", Timon's Verse: Timon is kicked out of his colony for being too rebellious and refusing to conform.
"Once Upon a Timon" (Timon and Pumbaa TV series): Timon is exiled from his colony when a snake carries off his colony's princess when he abandons his post while on guard duty. He is able to rescue her with Pumbaa's help, but decides to stick with Pumbaa rather than returning to his colony.
("Once Upon a Timon" was made into a comic as well. The cover is pretty amusing in hindsight, the way it proudly proclaims "Read How Timon Met Pumbaa!" Then when TLK1.5 was released, it's like Disney went "j/k lol!"
Pumbaa:
"All Mud and Motor Mouth" (The Lion King: A Nature Fun and Learn Series): Pumbaa's parents and siblings grow to dislike him because of how unusually obsessed with mud he is as well as his unpleasant smell. Eventually, he is forced to choose between mud and his family...and he picks mud.
"Home is Where the Hog Is" (Timon and Pumbaa TV series): Pumbaa is banished from his sounder because of his stink, leaving behind a female warthog named Sharla. When he and Timon answer a distress call from his sounder, he reunites with Sharla, and it becomes clear that they are deeply attracted to each other. Sharla asks him to rejoin the sounder, saying he belongs with them (and her), but Pumbaa still rejects her offer, saying that he's now a "lone hog", and he's willing to accept the hand he was dealt.
Zazu:
Friends In Need: After a young Mufasa rescues Zazu from three young hyenas, Zazu (a young hornbill at this point in time) tries to repay Mufasa by watching out for him. After Zazu helps Mufasa rescue Sarabi from a pit, Mufasa employs Zazu as his adviser.
A Tale of Two Brothers/How True, Zazu? (Six New Adventures): After Mufasa's father, Ahadi, employs Zuzu the hornbill as his majordomo (saying that she and her family will henceforth be stewards to the kings of the Pride Lands), she starts training her son, Zazu, to take her place when Mufasa becomes king. Sometime after Mufasa inherits the throne, Zuzu leaves the Pride Lands, leaving Zazu to take on the role of steward.
Rafiki:
A Tale of Two Brothers (Six New Adventures): Rafiki arrives in the Pride Lands when Mufasa and Taka are young adults.
The Lion King adaptation (Gina Ingoglia, 1994): During the presentation of baby Simba, Rafiki says, "It's as if I'm seeing you as a cub all over again" to Mufasa. (thanks to ClearGreenWater for telling me about this!)
The Hyena Trio:
A Tale of Two Brothers (Six New Adventures): The hyenas are depicted as adults before Mufasa's brother Taka receives the scar that becomes his namesake.
Friends In Need: At the beginning of the story, the hyenas are described as "young" and depicted as such. Later on in the story (it's not clear how much time passed), Mufasa's brother is called Scar.
Nala's departure from the Pride Lands:
The Lion King Musical: Nala leaves her pride after Scar attempts to seduce her, they all watch her leave.
"Hunt for Help" (The Lion King: A Nature Fun and Learn Series): Nala leaves the Pride Lands after dreaming about Simba, then speaking to Rafiki. His monkey friends help her get past the hyenas guarding the border by pelting them with rotten fruit, and nobody else sees Nala leave.
And lastly, a contradiction that isn't really a contradiction:
"King Joe/Great-Fighter":
"A False Ancestor" (Swedish TLK comic): A scrawny lion calling himself "King Joe" tells Simba that he is "great-great-great-grandfather to the present king" (Simba's great-great-great-great-grandfather), and brags about battling thousands of hyenas, and roaring so loudly that three trees fell over. When two parrots show up (hinting that Zazu may have sent them), they say that they know all about the Great Kings, and say that King Joe ruled Pride Rock when the hyenas tried to take over and he discovered the Elephant Graveyard. When they ask if he had two sons, the lion says yes, to which the parrots say, "Wrong! You had three sons!"
"A Heavenly Connection" (older, German version of previous comic): A scrawny lion calling himself "King Fearless" tells Simba that he is Simba's great-great-great-great-great-great-great-grandfather. He brags about saving his subjects from hordes of greedy hyenas and how his bravery earned him his present name, "King Great-Fighter". When two parrots sent by Mufasa show up, they claim that King Great-Fighter battled hyenas with tusks. When they say that he survived the first Laughing Malaria outbreak and had two sons, the lion agrees with their statement. The parrots then say, "Not true!" saying he had three daughters and Laughing Malaria doesn't exist.