My '19 Terrain did that about a month ago. First time that it happened. Hasn't happened since. Like you, a reboot (restart) resolved the issue.
Hello,Yeah, the dealer I tried initially claimed it was a quick 15 minute job, turned out to not be the case. I'm sure all the dealerships have the right tool, I suspect it's a matter of if the smart tech guy is working that day or not.
Swapping the radio over to a used unit isn't too hard, and if the radio was the defective part, you'll see the startup screen, and then a "LOCKED" message. The backup camera will work even though the radio is in "LOCKED" mode. But at least at that point it's pretty obvious that the radio was the issue. If you do buy a used radio off ebay, try to get as close a match as possible. Definitely try to get the exact same part number, but more than that, try to get it from a vehicle as close to yours as possible to account for any programming differences.
If you go onto Genuine OEM GM Parts and Accessories Online - GM Parts Giant and enter your VIN number, then search for Radio, it should show you the exact part number matching radio for your vehicle. Then search for that part number on ebay. Used Nav radios seem to go for around $200 on ebay. Non-nav radios seem to be under $100.