I have had this happen before, but this time it was a strange occurrence. I am playing AOF3 plus some extra mods. I want to say the culprit is simplex terrain (https://github.com/SuperCoder7979/simplexterrain). The really weird part is I (forcefully) crashed my game, booted it back up, then I could load into the world perfectly fine. Here is a link to all of my mods https://drive.google.com/file/d/1Z50BkVQab7vd3BhApxE4_twTXj1WOg2I/view?usp=drivesdk

A picture is on discord https://discord.com/channels/743126646617407649/811975125385740318/836715902480154634

Make sure the world type is set to simplex when creating the world

My specs (if it matters)
-RTX 2060
-Ryzen 7 5800x
-Graalvm Java 16
-6GB of ram dedicated

• UnlockExperimentalVM and ZGC are activated
• Fabric Loader 11.3

Try disabling parallel feature generation in the c2me config if you have it on. We are working on compat but as of rn it has some issues with world generation mods.
Edit: This is assuming you have that on, if not please let us know so we can investigate further.