I just experienced this last night on my way home from work. Still had 29 miles of range showing (about 30% charge left). Turning onto a busy road, I got the SSN warning, and when I stopped at the light a few seconds later the car died. Everything stayed on, but the accelerator was dead. I tried to turn the car off but it wouldn't respond. I put my hazard lights on, but of course other drivers were pretty annoyed because I was blocking a lane. There is no shoulder in that spot, only a turn lane, so I had nowhere to go anyway.
After a couple of minutes of desperately trying to turn it off and on again (hey, if it works for computers...) it finally responded. It turned off, and when I turned it on again it operated normally. I only had a couple of miles to get home.
I have 18,000 miles on my 2016 FFE. I have a relatively long commute (32 miles each way) and I charge at home (110v) and at work (220v). Most of the drive is on the NJ Turnpike, so 70-75mph. Thankfully the stall did not occur on the highway!
Conditions were cold but above freezing. Roads were dry. I can't think of any immediate environmental issues that could have contributed, although we have had a lot of rain lately.
Being the first time, I am nervous about it happening again, but I'm not upset about it. However, if it happens again I will lose confidence in the car. It's been great for me until now, but this is a major problem and a genuine safety concern. Reading others' experiences on this board, it seems like Ford has no clue why this is happening and thus has no valid fix.