There was a warning displayed before the film when I saw it, but apparently, it was not in the film provided by the studio but was added afterward by the theatres. Even with the warning, late-arrivers could easily have missed it with very serious consequences. I think it’s surprising that a big-budget film even made it to screens looking like that at all. A film that could potentially injure a viewer, where all the lawyers on vacation that week or something?
More info on the re-edit here.
Added information about Incredibles 2 theatrical release. Thank you CatBus!