Sorry for the delay, I was travelling for 5 days, this time with the convertible and also MyRouteApp.
I had the problems described above on a motorbike trip with a Pocophone F1 running Android 9 natively, i.e. without the use of Android Auto.
Unfortunately, my story of frustrations is not over yet.
We were travelling in the convertible for 5 days as mentioned and this time we have MRA on a Pixel 7 with Android Auto. (Android 15)
At first everything went smoothly. Paired the mobile phone with AA, started MRA and selected and started the route. No problems until the first break. After the break I started the car, AA established the connection, only MRA did not want to run on the AA monitor. The route was displayed on the mobile, the current location was displayed on the AA monitor, but the cursor did not move. As we drove on, nothing moved on the AA monitor, only the navigation was displayed on the mobile phone.
Stopped, shut everything down and restarted. Now it worked again until the next break.
After this happened to me several times, I downloaded the route from MRA as gpx, imported it into kurviger and continued with kurviger.
In kurviger there is an option to switch to the mobile phone on the AA monitor. And on the mobile there is a button to switch to AA.
I don't know anything like that with MRA, but it would probably have helped me in this situation.
The rest of the week we drove the daily stages planned in MRA on Kurviger and there were no more problems.