Ah, that's quite a bit different to your first pic. By mythical, I didn't mean you were imagining it, just that with such a low noise margin it was improbable you would see it again. They all seem to have a significant error rate though. I'm sure @BMarquis can advise, but that is frequently a bad cable joint somewhere, and common that it is at the consumer end when on the upstream. Realise it's a fairly new build, but it wouldn't hurt to double check there's nothing amiss in the internal wiring, as that would account for erratic connection speeds and high error rates.