I found a very strange bug, don't really know whats going on, but having both CraftTweaker and ZenithAttributes together makes all block drops vanish from existance, meaning when the player breaks a block, it's loot doesn't drop.

Removing either one of them solves the issue.
I don't know if this will be much of a help, but here's the log:
latest.log

The issue has been fixed upstream, TheWinABagel will need to update PortingLib.

Updated to latest porting lib as of 0.2.0

Exactly! I have the same problem😗

me too

It seems to be all loot tables. This mod's loot attributes must be doing something unexpected.

Still happening with zenith_attributes-0.1.2 and CraftTweaker-fabric-1.20.1-14.0.28

The issue seems to be upstream, in porting-lib
(note that zenith_attributes-0.1.5 has loot-2.1.1102+1.20-entity-refactor.jar)
Fabricators-of-Create/Porting-Lib#77
CraftTweaker/CraftTweaker#1702