This bug was very weird, I've only ever encountered it via pre-generating my world but this is very much possible to stumble accross a region that will do this to the server. Essentially, after a certain amount of time pre-generating or exploring a world you will get error messages about POIs, not a big deal in and that of itself but typically after these error messages the server just COMPLETELY stalls and refuses to run, it wont crash it instead will just hang there

Here is what the logs would look like: https://imgur.com/a/Eov6PAz

Notice the 3 red lines and POI, When i teleport to these POI's they are ALL always just the Artifacts mod's underground campsites, it doesnt matter if mimics are enabled or not, i tried that already, and in fact I've also tried this with the campsites entirely disabled but it still appear the server stall happens (Though, the POI errors do seem to stop)

This is the world seed i originally tried this on: 3259978356817320241

But, in my tests it appears this happened on 3 different worlds of mine, they would generate fine and then suddenly never start generating again. One server made it to 70k chunks generated before this issues, another made it to ~330k and another was ~110k ish, this will honestly happen on any seed in this modpack if you let it pre-generate long enough (Which, isn't long at all, ive ran all 3 of these tests within the past 24 hours)

To reproduce this bug simply start up singleplayer (or a server) and use the seed provided above, then with the imgure link provided above choose any of the last 3 red POI error locations, and voila you now have to alt F4 to close your minecraft/server :D

Unsure what causes this bug, but it appears to only be severely consistent with pre-gen, i assume within the next upcoming days someone will come out and say something similar about their server stalling out while they were exploring lol

Fixed in 2.37, for anyone who cant update ATM9 for unknown reasons, update Iron's Spell's as it was the cause of this bug