I'm having the same issue, the app at some point stops running, so I have to restart it.
I noticed that most of the times the list of contacts that were synced, weren't the ones specified by the App (I configured a special group called "Mazda"), but all the contacts on the phone, so I had to open the App to check if the car was connected with it, but instead of displaying the message "Connected to Mazda" it displayed the message "License Check Failed" and then "Ready". So I have to turn off and on the bluetooth, the car reconnects, this time using the service of the app.
At first I thought it was related to the "License Check Failed" message, but I read that it does the license check process at the first run and not all the time, while the app is running, so I realized the app stops running at some point (not listed at the RUNNING apps on Android).
What I'm doing is that, every time, before starting the car, I run the app, instantly it displays the "License Check Failed" and then "Ready", then start the car.
Galaxy Grand Prime
Ultra power saving mode: Off.
App optimization: Off.
I have activated the option for log creation at the app, I'll keep checking it until I see it is not running anymore and will post the log.