Forge version: forge-1.12.2-14.23.1.2559
Twilight Forest version: twilightforest-1.12.2-3.5.263-universal
Link to crash log: https://gist.github.com/LeLobster/af737ac9ee7d3e795d04fbaf59609ac1

Steps to reproduce:

1. Wander into the troll cave close enough to the Final Castle
2. Wait

What I expected to happen:
Generating Final Castle without freezing the game

What happened instead:
The game completely froze at 01:16, and at 01:28 I decided to kill the Java process because I got tired of waiting.
CPU's were constantly spiking to 100% usage
I'm seeing a lot of Maze of color * is getting a bit excessive., perhaps it's having trouble generating proper mazes?

I need seed and co-ords

Don't have time to play right now so did a quick look with NBTExplorer.
TF seed is the same as regular Minecraft seed in use?

edit: S:twilightForestSeed= in the .cfg is empty so I'm assuming it's using the MC seed.

RandomSeed: 4829061305580255573
Pos: 587.106938831521, 18, -153.779081649965

edit2: Loaded up the world today and it seems like the castle generated fine. (even though I killed the Java process earlier)
I went through it without issues and got to the final platform where I read the final boss sign.
Seeing a lot of this [Server thread/WARN] [twilightforest]: Final Castle tower has null for glyph color, this is a bug. in the log file though.

Besides the frequent desync/lag in the world during play and no final boss yet It was really fun playing through TF again. Last time for me was in 1.2.5 iirc. Fantastic work keeping this mod alive.

Also I wish I could mine the Castle Tower door blocks because they would look neat in the main base. :)

Same issue.
This error message crashes my minecraft server running 1.12.2 forge.

[twilightforest]: Final Castle tower has null for glyph color, this is a bug.
...

Those warnings generally don't result in crashes; if anything, the log spam might be a bit much, but not too much, though this no longer happens in 1.16.
World generation in 1.12 can be sluggish, and it is advised that mods such as Phosphor are installed to help mitigate this. If this persists in 1.16, feel free to create a new issue.