One of my students just experienced the same sudden pitch straight down into the ground after completing a loop in experienced mode and switching to SAFE mode. The same Apprentice had completed 7 or 8 previous flights that day with no issues. The student was on a buddy box and at 300 feet altitude when the dive initiated; she called out "I have no elevator". The instructor took over at about 100-150 feet altitude and also had no elevator control. After the crash the radio range tested OK at 150 feet; all control surfaces responding as they should.
The radio continues to accept rebinds and perform well. Apparently, there is no way to check or to update the firmware in the flight controller. I will post again here if I find a solution.