Hunger depletes when stood still

Vaniila server (private to home network). Multiple windows clients affected. Restarting server solves the problem, however it re-surfaces an arbitrary time later, usually days/weeks later, but has once started again almost immediately. When problem occurs, food bar depletes whilst player stood still (AFK), at a rate of about 1 icon per 20 seconds. This is much like MC-43601, however I'm not (knowingly) close to mobs, if I am, they are more than 8 blocks away, whereas MC-43601 suggests you have to be only a block or two away.