Great news , My 2017 High Country just did the same in reverse.
luckily I was backing my new Tritoon in the water when it happened.
Scared the crap out of me. Both feet did stop it, and a change of close.
I pulled it over 100 miles forward with no problems. Freaky
GM said it is not a Safety issue. So special warranty is issued.
I can’t use it on a rebuilt with 50000 miles.
Thanks for your input. I now know what to fix.
Reverse only ,Strange!!!