This appears to be a clear case of "home-cooking" by the French Open officials in this match.
With every other match already halted due to darkness, French Open officials forced Fognini to continue playing, at Monfils request, for 16 minutes after sunset in Paris.
Monfils was clearly hurting, and it seemed as though he didn't think that he would be able to go the next day. He wanted it to end that day, so he could recover the next day. So the officials made Fognini play in almost complete darkness.
There were many times in the last two games where it was obvious that the players could not see the ball coming back at them, so they lightly hit the ball directly to each other. It began to look like two players, in pain, warming up for a match.
It was not the right call by the official, and it was in no way entertaining for tennis fans.
Watching the match live, it was clear that the official was influenced by Monfils and the rowdy French crowd. He is there to make a decision in the best interest of the match and the tournament. He clearly did not do that. This is a black eye for the French Open.