With Bubmlezone Enabled
latest log: https://gist.github.com/Yourname942/453a7eeee008c1defdeb5b775f9034da

Steps Taken:

1. Select Play in TwitchApp
2. Select Play in Minecraft Launcher
3. Create new world
4. Enter world
5. Exit Minecraft
6. Repeat Steps 1-5 (but now for step 3, enter the world instead of creating new world)

With Bubmlezone Disabled
latest log: https://gist.github.com/Yourname942/8e56d20b79afad59a14f3b6063f01ab3

Steps Taken:

1. Select Play in TwitchApp
2. Select Play in Minecraft Launcher
3. Create new world
4. Enter world
5. Exit Minecraft

Minecraft 1.15.2
Forge 31.2.36
The Bumblezone (forge) 1.3.10

Note:
A) I encountered this error when I created world 1 (ie. a new world)
B) I tried to recreate this issue by deleting the previous world, and then repeating the process (steps 1-5)
- result: I did not see the error until I exited Minecraft (step 5), relaunched Minecraft, and then reentered the world.

This does not seem to be a Bumblezone issue but another mod's issue. Someone is probably not registering their dungeon properly or something. Even worst, this person registered their piece under the Minecraft namespace which is a big nope.

Your best bet is to try and find who's mod "minecraft:bigdungeon" belongs to and give them this bug report. The issue is, idk who it might be.

Oh it looks like it's Quark and someone has opened an issue with them as well
VazkiiMods/Quark#2410

Thank you for the replies, I'm glad it may not be an issue on your end.

Yeah. Vaskii found it is caused by a crash with BetterAnimal being on with Quark here: VazkiiMods/Quark#2410 (comment)

I'll close this report now. :)