It seems to me, that the breakdown of the non-verbal cue environment is frequently a function of fatigue.
After a certain period of years or after a certain number of routines are imposed, it just takes too much energy to demand consistent obedience. Unfortunately, this leaves those routines in a broken state, halfway between useful and purposeless. The students sense that lack of seriousness and the routines become mere speed bumps, occasional interruptions to be tolerated but not respected.
One of the very first principles we established for raising our daughter was to draw the circle of rules tight enough to cover the major infractions but loose enough to need only infrequent enforcement. This was based on the observation and belief that kids have considerably more energy to chafe against relatively pointless restrictions than parents have to enforce them. This leads to the “Don’t, don’t, don’t… ok” syndrome that eats many parents alive. We try to only establish rules that we are willing to us overwhelming force to enforce. If it is not worth a major consequence, it is not a rule in our house.