This has been an ongoing bug for awhile. When fighting the two bosses needed to open the gates (I forget their names), The boss in the lower arena will disappear if everyone fighting him dies, making progression impossible. The only solution at this time is to reset the entire trial and hopefully not die a second time. I do not know if this bug also appears in the normal version of the trial, as I haven't had a TPK from him, but that would be something to look into.
@Djennku, PCNA.
Grand Master crafter, all styles and all furnishing plans known pre U41.
Vamp and WW bites available for players.
Shoot me an in-game mail if you need anything, happy to help!