Social.ReportScore (returns no error, but score isn't shown in the leaderboard)

Unity: 2018.3.6f1
iOS: 12.1.4

I'm updating an older app from 2015 (so I'm sure, this code worked a while ago). The Social.ReportScore succeeds, but when I show the leaderboard, the score isn't there. The player is authenticated, I've also tried 2 different game center accounts (one already had a score in the leaderboard from old tests, one had no scores).

Code (CSharp):

1.             Social.ReportScore(score, leaderboardID[CurrentLevel], success => {
2.                 if (success) {
3.                     CAHelper.Log ("Score reported with success");
4.                 }
5.                 else {
6.                     CAHelper.Log ("Score reported without success");
7.                 }
8.             });
9.  

 

Problem found! I've used a leaderboard-ID that was an ID of a (still existing) game center group, but the app had been removed from that group...