BLUEMOMENT

Anchored last night in the Otter Pool. Previously, with my trusty Chinese copy CQR copious quantities of mud came aboard when I hoisted the thing. This time with a Knox it came up almost completely clean. I hadn't budged since I dropped the thing so presumably it works but there's something wrong, isn't there?

My Knox had mud on when I got it aboard at Ardminish this morning. I thought I was in sand!
Never budged apart from the 90° change in wind direction, 15m chain in 3m water

Yes, that sounds like a serious problem. A serious anchor should retrieve at least 400kg of seabottom when you weight it, along with a cubic metre of weed and otjer rubbish.
I anchored overnight in Airds Bay (F7-8 northerly). We ranged about 10m either side of the directly down wind position according to GPS measurements, but on weighing, the anchor seemed stuck fast. WE took in as much chain as we could, It was about vertical and still holding (5m depth). Just sat like that for a few minutes and it came free, but failed to bring home much mud and sand. Rather poor I thought!