Leaderboard has not been calculated yet???

I have configured a leaderboard in a group, to display top 30 leaders in a role (experts), with no other restrictions. 

Before now, I had not configured any rules in this fresh install. I deleted the stock ones.

Last week, someone in the role (experts) answered a question in a group forum, and had their answer verified as the answer.

Today i created a new rule which I called Verified Answer. I did not find it intuitive to configure, but this is what seemed to make sense.

When "a forum reply is verified as an answer" "is true"



"award points"

Number of points to award 10

Award to user: Forum Reply: author. 

But when I recalculate the leaderboard, expecting at least the member who had a verified answer to appear on it, all i see is: 

Leaderboard has not been calculated yet.

(despite the fact that the leaderboard was updated (ie calculated) minutes earlier.

Very confused.

Anyone shed any light?