Mr. Zyrinx should randomly appear in BlackSpike Mountains, and Mr. Nebulon should randomly appear in BlackSpike Summit. Returning to one of them with the Havoc Seed in your possession triggers the proper ending.
Wandered in both places - running, sleeping, all with increased encounters rate (not sure if that affects NPCs), also did 1st and 2nd fix for the clock.
No dice. They don't even shows up in Locate Person spell.
I DO remember that sprite in your screenshots from previous encounter but not sure if that was him, it was somewhere around the time when my team was send to get 2nd tablet. And like any other encounter with NPCs - they should show up again when passing through but for some reason it's not the case?
Or maybe they're related to Lord Ahriman and kicking his shiny metal arse prevent bounty hunters from coming for me?
Based on the guide they ask for Black
item, have Havoc
item in my possession but iirc they are the same?
I got similar issue with Shriek, it was before he gave me 3rd task. There was a case when I could not trigger encounter with him no matter what, usually he shows up every time my team get through the city but that was exception.