[Sephiroth]

Upstream is fine.

Your reply leaves little remaining. If you are still tapping off the neighbour, that would explain the low downstream power levels, but the stats don't show any poor SNR or corrupted data.

If 100m distance, your downstream power shouldn't be that low. Your neighbour's stats might be useful in diagnosis.

If it stumps them, then it looks like I'm gonna be stumped too.

That leaves the cabinet tap point or something wrong with your cable to the drop point outside your house. The latter is usually resolved by a cable re-pull; the former is usually resolved by moving you to a different tap point. However, they already did the tap point thing by piggy-back off your neighbour..