POE 2: Second Ascension Trials

I did my second Ascension Trial for lvl 28.

I finished the trials and defeated the boss.
Afterwards I thought great time to teleport back and sell the stuff to pick up the loot from the boss. I could teleport out, but not back in. So my progress and the key to enter the trials is gone.

So I did the trials for nothing, like 10 loot pieces, super frustating.
They should warn someone if you use the portal you cant go back or anything else.
I dont get it why I couldn´t teleport in and out after I defeated the boss, because the trials are done.

FYI I stayed in the area of the boss, because of the loot he dropped and didn´t proceed to the area with the loot boxes etc.