Act 2 softlock — Horn of Vastiri missing (Trail of Corruption)

I am stuck in the main storyline due to a quest bug in Path of Exile 2. In Act 2, during the quest “Trail of Corruption”, the quest item Horn of Vastiri is completely missing. It is not present in my inventory, NPCs do not give it again, and there is no interaction available at Halani Gates to use the horn. Because of this, I cannot disperse the sandstorm and continue the story. I have already tried restarting the game, creating new instances of the quest areas using Ctrl + enter, talking again to all related NPCs, and traveling via the Desert Map and caravan to Halani Gates, but the quest remains stuck and progression is impossible. This results in a full softlock of the main quest.

But how do you have lost the Horn of Vastiri, if you haven't played the horn?
And when you travel with the Desert Map to the Halani Gates with the caravan, there is no exit to the Deshar area?
Or what does the quest and Alasa say? Look also at the Wiki page for The Trail of Corruption.