XCompWiz

Still no idea why BetterPortals would cause this issue, and the crash happens in vanilla code. You could make an issue with BetterPortals to see if there's help from that...

That's odd. Can you reproduce this with just Mystcraft?

I wrote up a wiki page that may help with getting info on this : [Bug Reporting Best Practices](https://github.com/XCompWiz/Mystcraft-Issues/wiki/Bug-Reporting-Best-Practices) Looks like it might be a mod conflict with the baseline...

It's apparently a server hang and there's a mod that's killing it when it takes too long (ServerHangWatchdog). It might be that a dimension is failing to generate quickly enough....

Pastes are dead. See [Bug Reporting Best Practices](https://github.com/XCompWiz/Mystcraft-Issues/wiki/Bug-Reporting-Best-Practices) for a process of determining where the conflict is. :)

This callstack is all vanilla. You'll need to get this to the VanillaFix dev(s) to get it looked at from this direction.

Is it just this combo of biome and flat? Does either the biome by itself or Flat by itself produce the issue?

That would make sense. I'll note this for the instability rework. :)

There are a lot of mods installed here. Especially a lot of core mods. Can you produce a minimal test set? [Bug Reporting Best Practices](https://github.com/XCompWiz/Mystcraft-Issues/wiki/Bug-Reporting-Best-Practices) may help. Crash appears to...

I don't have an easy way to colorize the BOP grass, but I can try. As to why the biomes are barren... can you direct the current devs of BOP...