Yes, and according to Karl Jung, it coincides with moments when a people a undergoing trauma, huge changes, etc.
WWII, suddenly you get Foo Fighters. Cold war and nuclear war terror, they are everywhere. Unmoored and scared people “see” things.
“That doesn’t explain many of the stories.
Humans have been seeing “weird stuff” ever since they came out of the caves. This guy has a huge chronology of this—focusing on weird creatures of every imaginable description:
https://www.amazon.com/Humanoid-Encounters-AD-1899-Others-amongst/dp/1542722055
Science just dismisses all of this stuff as “anecdotes”, but it may well be that Occam’s Razor is just chopping off our own heads.