Here is the crash report https://pastebin.com/RiEutwNj

I WOULD take a screenshot, but this problem causes a crash on join. I'll describe my setup

Chest with extractor on it, pointed directly above a belt to move the items away. Simply placed brass casing to reinforce the belt (with no items on the belt btw), and now I can never join my world again without immediately crashing.

Duplicate of #327

There are a few ways to fix the world, the probably preffered method:

Go to your world save, and in serverconfig/forge-server.toml change the removeErroringTileEntities to 'true'. Load world, destroy the belt you placed the casing on manually, exit. Change it back to 'false' (you don't want to play with it on 'true'), and enjoy your fixed world.

Though as stated in the little comment above this variable BE WARNED THIS COULD SCREW UP EVERYTHING USE SPARINGLY WE ARE NOT RESPONSIBLE FOR DAMAGES. :)

Or, I've made a video on removing the erroring blocks. This seems to work well if the error is coming from something, that is not a tileEntity, but takes a bit more effort, and can cause more damage than the solution above. https://youtu.be/IgwamW7Ckmk