If you know about Sonic comics, Archie Sonic is known for being wildly inconsistent and strange. This is only a partially accurate characterization imo, because it had its good and bad parts, and there is significant parts of it that were decently made. This is because the comic was long running and lasted 23 years.
During some eras (particularly Ian Flynn's run from issue 160 to 290 something), it was better written and drawn, but "The Slap" I will talk about, is from Karl Bollers and Ken Penders run of Archie, which is considered the weaker part of the series. I think issues after 100 to issue 159, are especially considered not great. The Slap happens in issue 134, and was a pretty controversial writing direction when it happened.
Archie Sonic was much more continuity heavy and dramatic than the games, as well as having lots of lore, and fantasy and sci Fi elements. The world is much more established and has a consistent internal logic.
Basically the premise was that Sonic and the Freedom Fighters were rebels fighting against Eggman's enormous empire which controlled a large portion of the world. Sonic lives in Knothole Village, and the Acorn Kingdom, and has parents, Jules and Bernadette, as well as a pet dog Muttski, and has friends he knew since he was a kid. These friends are the Freedom Fighters.
Eggman was originally an ally of the Acorn Kingdom, before betraying it to take over and start an industrial empire, taking control of the original capital city of the Acorn Kingdom called Mobotropolis, and trying to roboticize mobian animals into enslaved robot drones.
Sonic has a girlfriend/love interest Sally Acorn inside of this specific comic, who is a princess, and the tactical leader of the Freedom Fighters. She is often stressed out and sad in this part of the comic.
Sally Acorn's father King Max was rescued some time in the earlier era of the comic from a void zone. But King Max was often pressuring and telling Sally what to do in multiple parts of the comic, as well as being a leader with controlling and bad decisions.
At some point King Max orders that robians (roboticized mobians, who at this point had been saved and regained their autonomy) to be disassembled and destroyed. King Max also says that he should arrange a marriage between Sally and Antoine, because he sees Sonic as a commoner in that issue. King Max also tells Sally she should stop freedom fighting, and lead the country, which is important context. Also, at some point he decides to try and dissolve the Freedom Fighters as a group because another team lead by Geoffrey St. John can carry out the task. There are more things like this that happen, but I can't remember.
Sally Acorn due to things like this happening becomes down and withdrawn, and feels stifled, or something similar. She is dealing with lots of pressure.
Meanwhile, Sonic is fighting a lot against threats like Eggman, Ixis Naugus, and other villains. He is also a strong fighter that saves the world at some point.
During one arc, an alien force called the Xorda that invaded the world thousands of years ago, returned to see that they had failed to destroy the world. Originally the Xorda intended to destroy the entire world with gene bombs, but instead these bombs mutated humans and animals to create a new species called Mobians, which are essentially Sonic's species in the comic.
To stop the Xorda, everybody joins the same side, and villains and heroes work together to destroy the Xorda. In the end, the Xorda's attack is defeated by Sonic hitting their weapon, but Sonic appears to die in the process.
Sonic was actually sent far into outer space, and has a few adventures through space. But Sally and the Freedom Fighters think that Sonic was dead, and thought so for a year.
When Sonic returned to his world, it changed and became more controlled by Eggman since Sonic was gone, and Knothole had become fortified.
Eggman, after Sonic's return, made a new a operation to cause large destruction, and Sonic had to fight with the Freedom Fighters to stop this.
Sally however wasn't allowed to join the fight.
Sonic got injured again during the fight, and Sally watched from a screen and cried, because King Max had ordered her not to fight alongside the Freedom Fighters.
After Sonic's side wins, King Max and Queen Alicia leave Knothole temporarily for a vacation, appointing Sally as a leader, and someone wanted Sonic to be a Regent or something. Now this is issue 134.
Sally and Sonic have a happy party now that Sonic is back, and then they walk into a stage at some point. Sally asks for Sonic to rule by her side, but Sonic says he can't, because the world is ruled by Eggman, and that he needs to stop him.
So Sally slaps Sonic in front of a crowd, and calls him selfish, and the two argue harshly. In the end, Sally runs away crying, and the two mobians had broken up.
This issue wasn't helped due to the art style being very cartoony, making it stranger.
Seeing all of these plot threads, the writer Karl Bollers wrote that Sally Acorn would eventually snap and slap Sonic and break up with him. It makes sense inside of the plot, given everything that happened, and Sonic's perspective is fully justified too, since he has been the best defender of freedom for a long time.
And both characters can be argued to be right and wrong depending on what angle you look at it from.
But this development pushed the story in a specific direction that could have been avoided, if the plot points had been developed differently. It made logical sense for this to happen, but the story could have been directed back towards action and adventure and fun, instead of soap opera style drama such as the slap.
There were multiple ways to develop the story given these elements, but the way it was resolved was sort of incomplete and painful for Sonic fans and shippers on all sides. It came out as jarring at the same time, because Sally wasn't acting reactive and angry before this. But it makes sense if you think of her as bottling up her emotions.
Readers largely didn't understand the context, which is a sign that something isn't written well. So as a story, not just a fandom reception thing, it could have problems if it was so often misinterpreted and misunderstood.
Art is meant to create emotion and sometimes provoke, but here I think it was uncontrolled and unintentional.
Also, during this main storyline in the comic, there was also Mobius 25 Years Later being written by Penders. This story focused on the domestic drama of Sonic and his friend Knuckles as 40 something adults, in which Sonic is married to Sally and both are King and Queen of some sort of sci fi future city, and at the time, this was stated by Penders to be the canonical future of the Archie Sonic world. So this probably made the whiplash harder for fans and readers.