I have no idea what people are talking about.
I’ve had my Bolt for 1 year now (14,000 miles) and have not ever considered this a problem with the radio.
It works the same as every other car I have owned.
It even has a nicer feature that many dont. The “Maximum Startup Volume” can be set. Although oddly, not to zero.
If your kid drives it the night before and had the radio way up, and forgot to turn it down before exiting, the car will automatically reset the volume to what you set.
Mute is designed as a temporary setting as it should be. It has ALWAYS been a temporary setting in every car I have owned. (Maybe 6 or 7 cars in 20 years, so not that many.)
Oddly, now that you all got me out in my car “testing” I find the mute IS retained after a power down and restart, if the restart occurs within x number of minutes. This may explain why people say mute sometimes works. It works for those quick trips to the mailbox or ATM machine if you get back in within a certain time frame I guess. I don’t care enough to figure out the time.
The 3.5mm plug in the socket seems like a simple fix to me though, all things considered.