What movies were originally supposed to be sequels but ended up as completely different, unrelated standalone films?

IMDb trivia mentions Vertical Limit was originally meant to be a sequel to Stallone’s Cliffhanger but was later reworked into its own thing.

Yeah, you can see some parallels. Someone close to the main climber falls to their death in the opening, he gets blamed for it, is consumed by guilt, gives up mountain climbing, but later has to return—among other things. Even so, Vertical Limit is totally different—its own thing.

Now, this bit of trivia got me wondering—what are some other movies that were originally planned as sequels but were later reworked into their own thing?