Some franchises go to amazing lengths to ensure that their continuity is perfect, leading to amazing pay-offs for fans when details are brought back for twists and surprise endings. However, many are less fastidious, especially if sequels are written or produced by different people, or if films are rebooted to serve a new Director's 'vision' of the story.
Many of the films on this list have tried to go in a creative direction, then written themselves into a corner. So have either messed with the timeline in order to fix the problems, or given up entirely and rebooted the whole series, ignoring the previous continuity.
Television spin-offs are another factor that can create problems, as they are often designed to give a fresh perspective on a story, and usually involve a different production team and actors. They are also frequently set in the modern era, so narratives from the original films (or books in some cases) need to be updated to be accessible to a modern audience and include updates in technology.
Lets try and untangle the web of continuity timelines of some of the worst-offending movie characters...