Had the same happen to me on my 2018.
Everyone I read is a 2014.
I lost all engine power going at 70mph on highway and all instrument in the dash went dark for about 10 sec.
All came back on just like if I had just turn the key on. It beeped, all lights came on and engine regained power by itself.
I notice a very faint electrical burn smell just prior to this happen.
The Generator was ON and both ACs were going at full power, that did not go off. Did not notice if the radio also turned off or the headlights, I was too preoccupied on what to do next.
Drove some 1500 miles after that and no events.
I did check the switch at the batt and it looks fine, no burn indication or any indication it got hot.
I did talk to FR and Freightliner and they said they never heard of such failure.