Have you tried to temp around the bad span to see what happens? Anything after the bad span is going to show an snr issue on a graph since the modems downstream are going to pass through the bad span. If you check your spectrum after the bad span you won't see it on your meter so that makes sense to me. You may be dealing with more than one issue on that run
This is CABL.com posting #292613. Tiny Link: cabl.co/mbohJ