I don't know about the dressage world but I do judge stock breed shows & 4-H, I wouldn't dare knit (or anything else for that matter) while classes were working. Seems rather unprofessional imo. I'm too busy watching horses work & taking notes (when I don't take a steward with me) to do anything else. On a break or between classes while the arena drag is being ran, that's different.
The footing, yes that stinks but it is what it is. I've ridden in and trudged through many while judging that I didn't necessarily like but everyone is in the same boat.
Sorry you had a bad show day OP. They happen. Just take it in stride and learn from it.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.