^No, they're definitely right about the Alien
franchises. I've seen those examples suggested on every other thread I've come across in searching for other suggestions. Yes, in both cases the original and its sequel were both science fiction, but they were in very different subgenres and styles.
I'm so frustrated -- I've got another example that I'm pretty sure happened, but I can't for the life of me remember what it was or figure out the right search terms to track it down. Now I'm thinking there was a TV show, probably in the '60s give or take a decade, that turned into a spy show after a season where it was in a different genre, like detective or lawyer or something. I wish I could remember!