It's possible that in the fanfic, Ron's sense of humor is changed into something mean - spirited. In the original books, Ron's humor is often light - hearted and friendly. But if the fanfic makes his jokes at Harry's expense in a cruel way, Harry would surely not be able to stand him.
One reason could be that the fanfic writer portrays Ron as overly jealous of Harry. In the original books, Ron has moments of jealousy but not to an extreme. If in the fanfic it's overdone, Harry might not be able to stand him. For example, if Ron is constantly trying to undermine Harry's achievements out of jealousy.
Another possible reason is that Harry is protective of their story. Fanfiction can be quite wild with different interpretations, and he might not like how some fanfictions try to rewrite their relationship. He has a deep - seated understanding of his bond with Hermione, and fanfiction that messes with that can be hard for him to tolerate. He might think that the real story is already great and doesn't need these made - up alterations.
One reason could be that the fanfiction changes her personality traits. In the original, she's kind - hearted but in fanfic, she might be made mean. Harry, who knows the real Molly, won't like this new version.
In some fanfics, Ron could be influenced by dark magic or dark forces. Maybe he gets cursed, and as a result, his mind is twisted to turn against Harry. It could start with small acts of undermining Harry and escalate to a full - blown betrayal. This is an interesting concept as it shows how external forces can change a character's nature.
Fanfiction can sometimes deviate a lot from the original story. It might be that the official creators or those in charge of the Harry Potter brand don't want the characters to be misrepresented in fan - made stories, so they restrict access to it for Harry or anyone in the context of that world. Another aspect is that some fanfiction may have a negative or unethical undertone, and to protect the integrity of the original story, access is prohibited.
One possible reason could be that he was injured during a battle with dark wizards. Maybe he was hit by a powerful curse that affected his legs. Another reason might be related to some kind of potion gone wrong. For example, if he accidentally drank a potion that had negative side effects on his motor functions.
Maybe in the fanfic, there could be a misunderstanding between them. For example, Ron might have accidentally broken Harry's trust in some way, like revealing a secret of Harry's that he wasn't supposed to.
The fanfic might be set in an alternate universe where Ron has a different personality. If this new personality clashes with Harry's values or his own personality, then Harry may not like Ron. For example, if Ron is made to be more self - centered in this fanfic, Harry might find it hard to get along with him.
Another reason could be a misunderstanding. Maybe he overhears something Harry and Hermione say and misinterprets it as them not wanting him around anymore. So, in a fit of anger and hurt, he leaves. This can lead to a lot of angst and drama in the fanfiction as the other characters then have to figure out how to get him back.
It could be a misunderstanding. For example, Ron might think Harry did something really bad to Hermione or their other friends. Without proper communication, his anger could lead him to punch Harry. Also, if there was some sort of magical influence or dark magic at play that affected Ron's judgment, that could be a reason too.
One possible reason is copyright infringement. Parseltongue is a unique creation within the Harry Potter series. If a fanfic uses it without permission while charging, it's likely violating the copyright of the original work.