papi lights

Hi guys , before i posted this i did a search but couldn't find anything . Today i made 2 flights from eheh to lepa and the return trip .On final approach i used the hud , papi lights were visible , but they suddenly disappeared in the hud .When i clicked the hud back up the papa lights were back , clicking the hud back down removed the lights again , so i couldn't see the papi through the hud . Best regards ,