dungeon bug
Wolf- qT- quantify-GIMME NEW DUNGEONS
I don’t believe this is a bug. This is likely a consequence of no one owning the dungeon any longer. With no one owning an instance and no one being in the instance, the servers likely “close it (idk what the appropriate term would be here)”.
^ this
But yes it is very anoying if you want to try the real challenge of dungeons in GW2, doing it solo.