Regarding the Watchdog firing... we expect the CAN Do to be "configured"
   by the IHU every 20 mSec (50Hz).  If this is happening the Watchdog will not
   fire.  So, as Bdale pointed out, set your CDNC software to send configures
   at, say 2 secs and you won't see any Watchdog firing.  It would also
   be good to see if other issues are seen while there is CAN traffic.
   Because you are using the less-capable Serial CAN I/F you can't run
   at a full 50Hz rate but you can probably crank it up to 5 or 10Hz and
   run just fine -FYI.