It may be due your phone's text-to-speech app settings.
I checked my wife's old S6 phone. It's no longer activated, but I can view the settings. Try changing the Text-to-Speech setting to use the Google text-to-speech, instead of the default Samsung text-to-speech, to see if that works.
After reading your post yesterday, I checked the text reading feature on my 2018 Leaf S today. On my car, the system only reads the text sender's name and message; I don't even get a date or time read. I have a OnePlus 3 connected to the car via Bluetooth.
2018 Nissan Leaf S w/QC
Placed in action: 9/2018