My understanding from reading an earlier explanation from JPL was that it appeared the issue wasn't so much from the missing frame itself but rather the software not being tolerant of the frame count being off.

IIRC, it seemed more like a missing test case or scenario in the software validation suite might have been the ultimate root cause.

Agree. It's interesting that they don't treat the optical and gyroscopic systems as two separate sensors with the possibility to disregard one if it disagrees too much. A quick restart of the visual system would have been the most optimal solution #2020-hindsight