I could've sword it wasn't because I had like no trouble with him that fight, but I think that's just gameplay. We know nightless doesn't work if there's something actively obstructing the sun like a sandstorm. It was clear they needed help to handle Gawain so considering the context I would think it's mostly likely his sun buff wasn't active. Maybe Simba's boost amped him somewhat outside the sun but not to the same degree.