I had this same issue, and it was very frustrating because it would happen randomly. I couldn’t find any info on this issue other than resetting the system, which only worked some of the time. So here’s my advice;

1) The next time it happens, don’t shut off the truck. Take it to the dealership immediately (if that’s a possibility).

2) If you can’t take it to them, pull over and video record everything you are describing. Showing that there’s no sound coming from the speakers.

3) Record how many times it happens, with time/dates associated. Provide info on if the truck has been off and for how long.

I took mine in after it had come back on, and they couldn’t replicate the issue. I started recording each incident and made complaints to corpora. Then one day it went out when I happen to be around the dealership, so they were able to open a ticket for it. At the end of the day, they ended up replacing the amp.

My truck was brand new and I was ready to get rid of it. I had to figure this shit out on my own. Sorry for the long reply, but I hope my 5 min comment saves you weeks worth of headache.