SUMMARY
Raid bar appeared spontaneously.

What happened?
I was in one of my villages and the raid bar appeared. I did not have the Bad Omen effect on me and was in my village when it occurred (did not enter the village.) I had not been involved with a raid for a long time (more than 100 minecraft days.) I have had Bad Omen before and have triggered a raid entering a village I found, I know how it happens.

I traveled around and through my village, east, west, north, and south until the raid bar disappeared. I turned around and went back to the village. When I approached my village, the raid bar reappeared. I never found any illagers. Eventually, the raid bar went away. I never found any illagers.

My village has several Iron Golems and I wondered if they killed all the raiders before I saw them.

Later (several MC days) in the game, the raid bar reappeared without Bad Omen effect, and there were raiders. The Raid bar showed the number of remaining illagers as it approached 0. My Golems and I killed all of them. The last one fell into a pit and I did not find him for some time. When found he died.

I did not see villagers celebrate of the raid being finished. Again, it started without the Bad Omen effect.

What did I expect?
I expected a raid (even without a triggering Bad Omen.) The second occurrence included illagers, again even though I did not have the Bad Omen effect showing.

I realize that raiders travel and I may have been under attack by them finding my village by chance. The guide does not address this (https://minecraft.gamepedia.com/Raid)

Affected version - Minecraft Java Edition 1.15.1
OS - Windows 10
Java version - don't know

Steps to reproduce.
I do not know how to reproduce the results I experienced.

(How come searching for Raid in bug reports yields 0 results?)