iPhone slow motion video pixelated (poor quality)

I have an iPhone 11 Pro and the slow motion quality is soo bad suddenly. I feel like earlier my slomo videos weren’t so pixelated, but I just shot some in a river and the water and everything else is completely unclear, which shouldn’t be an issue with such a great camera. Is there a way to get my shot videos to be clearer (maybe a certain viewing setting?)

if somebody could tell me why this is happening and how to fix it I would be very grateful!