Right clicking with a brass case on a moving belt near a fan, facing away from another belt being observed by a belt observer caused a crash, I was able to recover by uninstalling create, loading into the world without create, then reinstalling create.

Modpack was Kreation 2 using the following mods: https://imgur.com/a/xArL7RY

Occured on version "create-mc1.15.2_v0.2.4c-all" updating to new version 0.2.4d still caused a crash

Log: https://pastebin.com/p6MKscNY

This is a duplicate of #327 and marked as resolved there.

Interestingly, I had the exact some problem.
I was trying to place a brass casing on a moving belt near a fan with lava when the game crashed and I was unable to join the world again without the game crashing again.
Like discribed in the initial post, I uninstalled create, loaded the world again and then reinstalled Create. But after joining the world all Create blocks were placed in wrong directions...so basically all my machines in the world were destroyed.
In summary: The World is lost.
I am using Create 0.2.3 with Minecraft 1.14.4 with forge-28.2.18

I was able to save the world by upgrading to Minecraft 1.15.2 using Create v0.2.4c-all, altough a lot of blocks were missing because of changed block IDs.

But after I tried to go on playing, the same bug happened again. The world is lost again.
I don't want to make world backups every 2 minutes.
Please make this bug high priority and fix it :(

This is a recurrence of #337, I've also posted short guide on how to fix the world file in that issue.