[Gameplay] Ekko ult in river bug

I keep having a problem where Ekko's ult does no damage in some parts of river. I have only noticed it at the edges of river. I think it might be because of the geometry in the river or the height difference between river and the ground next to it. It might just be that it didn't hit when it looked like it should have since you can't see part of his ult because it gets overlapped by the ground next to river; but it has happened several times when I was right next to an enemy. I have also had the same problem with his W but not as much. I have had this issue on both sandstorm and base Ekko. Please tell me if this is an actual bug or not.