It's pretty easy to design a really bad FADEC/engine controller and the best way to do this is give the job to a bunch of electronic engineers!
On the other hand, a robust, reliable system starts with a bunch of FMEAs and other dull paperwork exercises, driven by someone who understands both engines and electronics. Since this is relatively rare and especially unusual in the GA/Aerospace industry, its more common to find controllers that react badly to failure modes, of which interconnects are probably the most common factor.