It's not like the issues between the ACB and Mohammad Shahzad propped up all of a sudden. The relation was cold for the last 2-3 years and it reached a breaking point when Shahzad was omitted from the world cup squad. After that he threatened to retire, but the selectors refused to give in to his demands. This is what happened back then:
https://gulfnews.com/sport/cricket/afghanistans-mohammad-shahzad-threatens-to-quit-cricket-after-world-cup-axing-1.1560242367669