2012 Plug-In Prius with “short” problem

After a session with mice in my heating system this Winter I found that I have an intermittent (unfortunately) problem. According to the dashboard light I lose these three things: regenerative braking, ABS, and traction control, all at the same time. I was plagued with this through most of our Winter, but every time I took it in to be serviced the lights would be out and I was told that they could not trace the problem, even after many hours of searching (at Toyota dealer rates). Since Spring and into Summer the lights are generally off, but do come on at seemingly random times for short times (a trip or two). I can see nothing unusual that initiates the event. Twice it was just starting the car in our garage and once it was just driving on a straight and level (and smooth) road,

Does anyone have any suggestions as to where this problem might be? What do these events have in common (and, no, the wheel sensors apparently check out okay, and a frot gearing was replaced)? None of these are major issues, but the car will not pass inspection if the lights are on.