Aborted Arc: Obviously, for a long-running title, a few of these happened.
A 1995 story had Johnny quitting the team to join the Fantastic Force to keep an eye on the teenage Franklin/Psi-Lord. Before that could happen, Force was canceled and Franklin returned to his younger form.
When the book was canceled in 1996 for Heroes Reborn, it left up in the air a few plotlines like Johnny and Lyja possibly getting together again.
Scott Lobdell had big plans for the Heroes Return saga such as hinting the cosmic rays might transform the FF more. But after just three issues, he was let go and those plans ended.
Stan Lee really loved the Silver Surfer, having acknowledged him as a favorite many a time, despite his runs never lasting as long as bigger Lee creations like the Fantastic Four or Spider-Man. Notably, one of Lee's all-time favorite comics he ever wrote was a Silver Surfer story.
The Fantastic Four were a hit when first released, but in time they were overshadowed by Spider-Man, the X-Men, and the Avengers, and never reached their level of success. Still, Marvel never ceased to publish the title because of low sales, and always had a place for them (the 2015 cancellation was a negotiation tactic to make Fox give up the cinematic rights... meaning, it was ultimately to get more of the FF, rather than get rid of them). They were the first comic of Marvel in the silver Age, the one that kickstarted the Marvel age, and Marvel has always been grateful for that.
Cult Classic: The Fantastic Four have never been high sellers since the 1960s. The runs of John Byrne and Jonathan Hickman are no exception, but they are beloved by fans.
Meaningful Release Date: The Fantastic Four have their 60th anniversary in 2021. As a result, Marvel released Fantastic Four: Life Story (the team reimagined in a world without Comic-Book Time), the Fantastic Four Anniversary #1 (a giant-size version that replays, scene-by-scene, Fantastic Four #1 and Fantastic Four Annual Three but with modern artists making a page each one), and the ongoing comic at the time made a time-travel arc that would revisit all the eras of the team.
Same Surname Means Related: Nathanial Richards shares a name with Kang the Conqueror. They're different characters, though it's strongly implied the man who would become Kang was not only his direct descendant, but was inspired by the time-traveling ventures of his namesake who created the very utopia he grew disenchanted with, making him something of a Legacy Character.
Similarly Named Works: The group shares its name with a 60's soul band. The coincidence was acknowledged (and joked) in Doctor Strange in the Multiverse of Madness, when MCU Strange, after being introduced to Earth-838 Reed Richards, presented as a member of the Fantastic Four, snarkily refers to the superhero team as if it were the music band.
Screwed by the Network: The reason the comic series came to an end in 2015? Blame Ike Perlmutter. Due to him being very bitter over Fox owning the film rights, he canned the series so that the 2015 movie wouldn't get any publicity from Marvel. Fortunately, after Disney bought Fox, the Four were revived in a new comic series in 2018.
Writer Revolt: At least one version recounting the team's creation explained that it was meant to be Stan Lee's final comic work, filled to the brim with Author Appeal as a way to get back at Martin Goodman for pressuring Lee to Follow the Leader and write stories based on whatever genre was popular at the time. If the book had been a failure like Lee anticipated, he would've readily retired from comic book writing to pursue writing for Hollywood.
. The coincidence was acknowledged (and joked) in Doctor Strange in the Multiverse of Madness, when MCU Strange, after being introduced to Earth-838 Reed Richards, presented as a member of the Fantastic Four, snarkily refers to the superhero team as if it were the music band.