Can't go back to trial of Sekhemas.

Can't go back to trial of Sekhemas, after completing the 4th trial and killing the boss, I got a ping that somebody wanted to buy a more expensive item that I was selling. So because the option was there, I teleported back to town, into my hideout, did the trade, came back to the portal only to find out you can't interact with it.. The portal is there but you can't go back through it again...

I have exactly the same problem atm