AMP URLs are no longer recognized in Top Stories, it seems google changed some syntax
For example
link 1 "Yahoo" in top stories, the url is "https://www.yahoo.com/amphtml/entertainment/novak-djokovic-calls-wimbledon-ban-130817359.html", which is AMP url
while link 4 "Reuters" is not
BTW, it was working fine till 4/13-14