I thought of that too… so I copied my database to single-player and disabled all the mods one by one 
No change… I see a few others complaining of this too. I replied to this thread I found here No event on my four private servers - #2 by Xevyr
Idk, it’s just weird, before the small update a week ago Grave Matters was triggering every single time I went there for example, now it’s doing the same thing as this and just refuses to start.
I even wondered whether it’s by any chance linked into maelstorm settings… but even those are enabled as normal since I left them as default in the config despite not being a siptah map 
Who knows… maybe it’s related to the amount of people online on the server
Edit:
See? here’s my “first attempt” I went there on my real character on the server, I’m the only one online atm. I was hoping to catch my first encounter with this event on camera to see if me and the thrall can easily handle it… I’m even on a farming build here 
I set up a bedroll… I showed off all the flimsy equipment we’re using and the thrall’s salted pork and everything… only for nothing to actually happen… lol
I got really confused since I haven’t seen the event yet I wasn’t sure whether it’s supposed to happen in the settlement… so I go and check the surrounding area too… but nothing happens
