As of 1.10, a few furnace event-related features seemed to have stopped working.
As an example : using a hopper on output COMPLETELY DISABLES the 'luck' factor of the ovens (which is done using
Here is the file where we use this method : you can see we aren't checking if an hopper is below the furnace.
Here is the issue that has been created on Slimefun's issue tracker. You may find there some useful informations :