So on Desktop, I can only reproduce this in responsive mode -- it doesn't seem to apply when I just resize the window. I can reproduce it on my S9.
Unfortunately, I don't think we'll be able to do anything significant about this. For me, the gradient appears and disappears. In many cases, stopping the scroll resolves it, though not always. This points to it being a browser rendering bug. I'm going to leave this open to try to produce a reduced test case, if possible.