As of v2.1.7, in Season of Discovery (other versions not tested) will only sort once per UI reload. Afterwards the message [09:58:25] tdPack2: Packing now is printed but nothing happens. No UI errors are thrown.

Thanks for the quick response! This happens on Classic Cataclysm as well. It also gives more errors:

I've disabled all other addons and deleted the settings file SavedVariables/tdPack2.lua and the error still happens.

Sorry, because the server is not open in China, I am not in a position to test the discovery season