Outofsynch. If the PAPI needs a warm up period before giving reliable signals, you would think that Air Services would warn of this via AIP. It it was a significant problem then surely PAL actuation would prove insufficient time for the lamps to warm up in order to prevent pink rather than red lights.
Occasional single or two lamp failure on a VASIS box makes almost no difference to the integrity. The light source appears a little dimmer, that's all. However if one complete box goes out of action due a major electrical problem, then that can quite misleading. Of course one box u/s on a PAPI would be misleading, too.