Date & Time: 12/4/21 5:40pm
Area and coordinates: Radz-at-Han

This is a bug that occurs when you go to speak with Vrtra at the end of The Jewel of Thavnair quest. If you enter the cutscene during a time when it is raining, the rain will appear along the wall next to Vrtra even though we should be completely inside of a building.

They're only raindrops so it's hard to see in a still image but I tried to point out the lines that are clearly raindrops falling through the walls.