Swiss tournament on Lichess Swiss had 5 rounds, but suddenly became 4 rounds. It's a bug?

I was playing this tournament on Lichess Swiss: lichess.org/swiss/WcoSrpJC

It was Classical increment 5 rounds, but at the beginning of the 5º round, after the countdown, the tournament suddenly was ended with only 4 rounds. It's a bug? Considering the points, there was chances of change on the result, and with the ending on 4º round favoured the players on the lead, and took the opportunity of the others.

As only 5 players were present for round 4, the most likely explanation is that it wasn't any better for round 5 and it was impossible to do the pairing.

Yes, just to clarify, in Swiss pairing rules it is forbidden to pair two players who have already played together in a previous round. Therefore if too many players leave before the end, these tournaments risk having to be stopped early.

I got it, that really makes sense, as i remember that some of the players were absent at the beggining of 5º round.

Thanks both for the clarification.

Yes.