Have the same problem. Played it 5 days ago, winning the first game. So now I'm at Niveau 1 Round 2 (only, didn't spend much time on this special event). I cannot play it because I have to unlock the previous round, but at Niveau 1 round 1 there's nothing to click.
Puntjeland, level 51
(I don't care much for this one, the Nation League change that you only have one day to play matches bothers me more).