Interesting. A switching malfunction appears to be the
only valid reason.
ICAO Manual for Preventing Runway Incursions.
5. STOP BARS. 5.2 PANS-ATM (Doc 4444) states “7.14.7 Stop bars shall be switched on to indicate that all traffic shall stop and switched off to indicate that traffic may proceed.” As such, a controller should never issue a clearance to cross a stop bar without first switching off the stop bar. The only exception to this should be when contingency measures are required due to unserviceability. An example of a contingency measure is the use of a follow-me vehicle.