Half of the contracts in the back of the curve have zero volume, so the exchange makes up a settlement price. If you only look at volume traded you should see this
You're quite correct! I have to remember this chart shows the last trade price, not the last quote. This was a good lesson for me. Next time I see a distortion in a fwd curve, it may not be a mean reversion trade opportunity. Just as likely to be a stale print.
Yeah, old prices that's what I thought as well. Exchanges are shit that way, they should provide better data. When related prices change by a lot, the last traded price isn't reflective of the value anymore in case of no trading.