This starting happening to me recently. Scared me at first thinking it was a hacking attempt but they just annoyed me for days. So I recalled what changed since it started happening. First, no changes on my Mac Mini. BUT I did login to my AppleID on my wife's MacBook Air through a separate User account on it. I figured that had to be the cause. So I logged back in to it then logged out of that profile, not my iCloud/AppleID, but the macOS User account on the MacBook. And to my relief the "password reset" notifications stopped on my Mac Mini!
I encountered this once before and it was a similar cause. Then I wiped my old Mac Pro 2009 and logged into my iCloud account on it.