The “UFO community” explanation (fwiw—I am _not_ endorsing it) is that the 1940s and 1950s “flying saucers” could be disrupted by certain types of radar or atmospheric conditions, and there were crashes as a result.
If you want to read further on that topic the best book (currently rare) is probably:
https://www.amazon.com/UFO-Crash-Retrievals-Investigation-1978-1994/dp/0359685080/
Thanks. Now that’s science fiction (1940’s radar brought down a flying saucer?). Maybe Covid will do them in, so we shouldn’t wear a mask or socially distance when encountering an alien.