What went wrong?
I went to Lightless Arbor dungeon and tried tier 4 for the first time. I used portal charm.
The boss killed me. The game offered options 1) respawn, 2) try again at the cost of 1 key.
I select to try again - and it did swan me in the boss room. BUT my character was without the ‘Pyre Amber’ - the main dungeon mechanic buff! So, it was impossible to do anything! The game simply ate my dungeon key and my only option was to teleport out with portal.