I had the same thing happen to my 2014 Energi SE Luxery. It had a check engine light on that was an O2 sensor verified by my mechanic. The Safe to Stop happened 4 days after that. Pulled car into parking lot shut it off would not restart. Left it off for 5 minutes it restarted and did not return. Took it to ford this week for O2 sensors, which are covered by the Hybrid warranty, but no other issues or incidents. My dealer did not see it in the codes because my Safe Stop warning cleared from the codes because of the 2 week delay to dealer for appointment.
