• Minecraft version: 1.14.1
• CC: Tweaked version: 1.82.4
• Fabric version: 0.4.8+build.155
• Fabric API version: 0.3.0+build.184
• Detailed reproduction steps: Clean setup with installed Fabric and Fabric API. MC without CC:T runs ok. After adding CC:T to mods folder, I got this crash report:
  crash-2019-06-14_10.59.59-client.txt

This issue might be related to the #269 issue on Fabric bug tracker, but I'm using vanilla MC launcher instead.

Not sure if you've figured this one out already, but another few mods I play with had the same crash on startup.

Epicurean Gastronomy's patch notes said:

fix a crash from Fabric registry sync due to how mixins handled re-registering items

Maybe that points you in the right direction if you haven't taken a look yet.

I'm afraid I'm no longer maintaining the Fabric version due to limited time and motivation, so this will not be fixed.