What if many UFO sightings are failed attempts to change the past?

An idea that sounds strange at first, but the more you think about it, the more it makes sense. Assuming that the past cannot be changed, it is possible that UFO sightings near nuclear facilities are actually failed attempts to neutralize nuclear capabilities. The UFOs manage to appear near these facilities, but fail to permanently influence (if at all) their functioning. Moreover, there are many UFO sightings all over the world, yet somehow there is not a single unequivocal photographic proof for the general public. What if the UFOs are actually trying to be exposed but fail again and again, because the past, where the exposure/disclosure happened at a specific point in time that we haven’t reached yet, simply cannot be changed?