I was amazed to find recently, while looking up something completely different on IMDB, Dark Blood, River Phoenix’s last film, released incomplete in 2012, nearly 20 years after his death.
Despite its incomplete state, a lot of IMDB review writers are quite enthusiastic about its quality … or at least, the quality it could have had, in an alternate world.
I have heard Apocalypse Now! cited as a film shot without an ending, but would personally dispute that. *The Thief and the Cobbler *has had a couple different cuts, one of them pretty embarrassing; I guess they saw that Aladdin was going to be released and they had little choice but to fish or cut bait.
The Twilight Zone: The Movie fits the bill as to the first segment. It had to be edited and the ending changed because of the filming deaths of Vic Morrow and two young children.
Another kind of incomplete I guess - when I saw Straight Outta Compton, I remember a scene late in the movie where Paul Giamatti says something to Eazy E, then says the exact same thing again a few seconds later. Like they left a second take in and forgot to edit one of them out.
For you Mystery Science Theater fans, one of their feature films 1965’s Monster a Go-Go literally has no ending. Basically the film was shot in 1961 but ran out of money half-way through and abandoned, leading to another director to buy up the rights to the unfinished film to fill in space for a double feature with one of his own movies. The result was they filmed about 15% more scenes with entirely different actors leading to massive continuity problems and major characters literally just leaving the movie without ever being mentioned again, as well as crucial plot points happening off-screen because they never bothered to film those segments.
The ending is the biggest mess, the film just kind of ends in the middle of an action sequence. The titular Monster is chased down to a subway then just suddenly disappears while the film suddenly ends and the narrator muses that maybe the monster wasn’t real at all and it was all the figment of someones imagination. So basically this was all a complete waste of the viewers time.