That's exactly my thinking. I've already placed leaf covers over the gutter downpipes but there's always room for sludge to get down. I think it's just a very shallow drop, if anything at all, so the rainwater just isn't clearing as fast. Gladly it's temporary and the water drops away quickly as rainfall eases.
Looks like a longer term fix as you suggest and I might see if I can stick an endoscope down the pipe just to check
