icloud keeps pop up for password
I got macbook pro on high sierra 10.13.6. Since the last time I change my mac's password, icloud keeps pop up to ask for my icloud password. I input my password like dozen of times over last 3 months and it never worked. My know my icloud password since I use it all the time on my iphone; and it is not about internet connection in office since I try it in many places, in office, at home, with 4G cellular network. It just keeps pops up to ask for my icloud password. What can I do now?
MacBook Pro with Retina display, macOS High Sierra (10.13.6)