Thanks, Snacko.  That's one of the first things I checked, but everything looked fine.  It's kind of a random thing though, so I might have missed it.  When I look at the RoF controls screen, I sometimes see things jumping all over the place; then it settles down, only to start up again at unpredictable times. 
I have another Bodnar board and a spare Hall sensor, so might try swapping in those components and see what happens. 
P