Blocking someone who is watching you removes the watch. Then they unblock thinking that if that person looks at their page they won't notice. They're just kicking their problem down the road, which is worse than just blocking someone outright. Then they get defensive when the person wonders why they did this.

It is an emotional manipulation tactic to direct the fault to the other person. Instead of taking responsibility and just blocking someone they don't like.

The number of people on my "Recent watcher" thing keeps going up and down like a blasted yo-yo with no one actually unwatch or adding a watch to my page 😓 messes with one's head

Yeah if someone does watch you then unwatch, it would show an unknown user in your watch notifications. It is possible that people watching you are hiding and unhiding their account, but that doesn't seem likely if you keep seeing your watched number changes constantly.