Stuck in Act 3 - Can't phase into Aggorat

Currently stuck in Act 3, Cruel at level 61. I'm at the point where you ascend the stairs into aggorat - "Enter aggorat and search for the Black Chambers". However, I can't click on anything at the top of the stairs; the portal just doesn't exist.

Anyone having a similar issue, or know a fix?

Did you try to restart the game and reset the map ?
Cause that's pretty weird.

Worst case, if you're no in SSF, ask someone on the global or a friend to give you the warp point for aggorat, to bypass the problem.

Did you leave the game after defeating Viper Napuatzi and then returned again later to find yourself unable to enter the next area (Aggorat)?

If you came back later, the area may have timed out and you entered a new instance but beyond the boss fight (which will have respawned). I can imagine that this might prevent you from accessing the next area.

If the Aggorat waypoint wasn't activated upon defeating the boss (in which case taking a portal to town might do the trick), you may need to repeat the fight to continue?

And there should be a checkpoint immediately after the Viper Napuatzi fight, so that after death (or disconnect) you haven't to replay this fight.