I made a discovery yesterday at my school. If you give the fluorescent lamps in some of the classrooms a tap they go out! Some need a slightly harder tap than others but me and a friend went round whacking them all with rolled up paper tubes (they don't need tapping that hard!) and about half will go out and stay out and the other half will extinguish and then re-strike. They work perfectly fine if you switch them off and back on again or sometimes come back on with another whack.

They're about 10 year old electronic ballast fittings, two of them extinguish after about 15 minutes of operation for no reason and some of the others extinguish and re-strike intermittently. The ballasts are obviously failing but why would giving them a tap cause them to fail?

Tapping caused intermittent loss of contact in sockets, what cause EOL protection to trip and shut them down. Then they need remove-reinsert the lamp and/or power OFF-ON cycle to restart them.