For 1.5+ years, the transmission will unexpectedly and suddenly downshift into 1st gear without warning. Which causes a sudden deceleration. No warning lights before it happens. It occurs randomly and at different speeds. It has happened over 20 times. I’ve experienced it happening at speed ranging from 35mph to 65mph. The gear shifter was in the drive position each time this issue occurred. The suv is the 2017 ford expedition EL with the 3.5L ecoboost engine with 6 speed automatic transmission. No check engine light before or after the issue (so no OBD2 code to read) a big yellow warning appears during/after saying ‘see manual’. Sometimes the issue will resolve in a few seconds. The suv has not been to the dealership yet for this issue. But i will be contacting ford today.