Hi!
I noticed that SublimeFileDiffs works well right after install, but when I restart Sublime Text 3, it stops working.
I have to remove and install it again with Package Control to make it work...
The console doesn't output anything.
I reproduced this issue with Sublime Text 3 (build 3047) on Windows 7 and elementary OS (a linux ubuntu-based OS).
Let me know if you want me to try something.