As I suspected, the protected side of the DoCraft function might not be allowed by addons at all.
Debugging:
I don't think there will be much you can do if it isn't erroring out noisily. I suspect because it is being called in a secure environment it is just silently failing because it isn't a Blizzard addon calling it. However, if you don't have Bugsack or Buggrabber installed, you might want to, and see if they see something.
Protected functions with no accessible code:
There is no DoCraft function in the accessible Blizzard code that I can see which could explain why there is no info on it in the wow api code. It's probably one of their behind the scenes code that is just called by valid callers.
It is only used directly in the xml file on the Crafting Button that you click in their UI.
https://github.com/Gethe/wow-ui-sour...rd_CraftUI.xml
Looking for that button control in the lua file to see if they do anything else with it and apart from enabling and disabling I also noticed this line of code. However, like DoCraft(), this GetCraftButtonToken() function doesn't exist anywhere else.
Lua Code:
-- Set the action button text
CraftCreateButton:SetText(getglobal(GetCraftButtonToken()));
https://github.com/Gethe/wow-ui-sour...raftUI.lua#L99
Did you try making sure the Blizzard addon is loaded to see if it is needed to have access to these functions? :
If you haven't already, you could try making sure that the Blizzard_CraftUI addon is loaded before using it's functionality.