>>2064I dont believe in the UFO cult, but Ill play Devil's advocate and posit an idea:
Our closest star system is Alpha Centauri - it's ~4,4 light years away, or 25 trillion miles.
We can assume that, should the aliens eminate from that system, even with significantly advanced technology, it will still take them some time to reach our star system. Even with speeds close to, or equal to light speed (assuming my math is right), it would take them almost 1 Earth year to reach us. Given the nature of space-time, however, time would still normally pass in their homeworlds - thus potential millenia would pass between their trips (scientists have posited that it would take our current probe systems about 18000 Earth years to reach Alpha Centauri).
This could thus mean that the UFOs we see are all from different 'eras' of technology. Compare, say, the first plane flown by the Wright brothers to the jet fighters used in militaries today - and thats merely a difference in time of over 100 years. Imagine what a millenia of concerted technological effort could do to the state of aeronautics development. Thus, the 'disruptive' UFOs could've been 'early generation' - prone to faults, crashes, forced landings, electromagnetic disruption fields. Our 'visitors' may have now reached a state in their technology whereby their vessels are nigh undetectable, not prone to crashing, etc.
This is all assuming that warp technology/faster-than-light travel hasnt been developed, though I would reckon it's a fair assumption that 'early' gen UFOs likely would not have such tech, even if later iterations do.
Again to reiterate, I don't believe this to be true, I lean more to the idea of inter-dimensional phenomena if UFO activity is indeed even real, rather than the traditional conception of interstellar flight, but I figured there may very well be a logically consistent answer to your questions, OP.
