TL-DR - I had to download a completely different SMS application (in my case, Textra) in order for text notifications to work properly.
I recently purchased a 2017 Silverado LT with Chevy MyLink (Android Auto) and as far as I can tell I was having the same EXACT problem. Everything worked great with the exception of sms notifications. I spent several weeks trying to research this problem and possible causes/fixes.
Some background:
- I'm on a stock Samsung Galaxy S8+ with Android 7.0 Nougat. When I first bought the truck, the notifications worked fine, then after about a week, I received several updates (in the truck and on the phone). As far as I could tell, this is when text notifications stopped working.
- Switched to an iPhone 6S Plus for a week. Everything worked fine, as far as notifications. Switched back to the Galaxy S8+, no notifications again.
- I factory reset my phone, and text notifications worked again for about a week or so. This time, no updates in the truck. Randomly, I'd sometimes get a notification, but what I noticed was that I only got them from people using iPhones. Thought this was really weird, but it put the idea in my head that it could just be the SMS application itself.
- Downloaded Textra about 2 or 3 weeks ago and ever since then, I get every single SMS message notification without failure. Android Auto displays a drop down notification and populates a banner that allows me to play back the message again or respond with a preset Driver response.
**Based on my research, Android Auto doesn't seem to handle MMS (i.e. group) messages very well and won't typically give you a visual notification. I've not really been able to test this adequately and can't confirm.**
Sorry to be so long winded. Just wanted to give as much info as possible. Hopefully you can try this and it works out for you!