Losing All Rewards After Completing Trial of the Sehkemas

Really pissed off right now as I just completed my first trial, the trial of strength to get my ascendency, and couldn't fit all items from the boss in my inventory so I portaled back to the caravan to sell, like I've done a hundred times, and even did previously during the trial. Turns out for some absurd reason the game won't let you back to the boss arena. It seems it considers the trial complete, and yet I can't get back to the treasure room, or use the altar of ascendency, so I'm just SOL. Quest tells me to use the altar, which I can't even get access to anymore. When you use the waypoint to get back to the trial entrance, you can no longer use the plinth to go back into the trial where you left off, it's just empty, like you never did anything. Am I missing something here? Or is the whole thing really this fucked? I can't imagine why you would design it this way, to lose progress entirely if you portal out. Only option seems to be to start the trial over from scratch. Is there any way around this?