What's really odd is everything works perfectly in the Android auto app but when plugging into the stereo it gets crazy. You would think it would work the same as the car if it was an issue with the phone.
What other phones have you tested?
Edit: I decided to go out to my car and test a few things. First I replaced the USB c cable I got from Best buy with the Huawei cable. I did have to re-engage the call screen like mentioned above the first time. Then I tested when I plug the phone in and unplug it. Unplugging it never made a difference whether the car was on or off. Plugging it in however did. If I waited to sync fully loaded before I plugged in, text messages wouldn't read. The dots came up but never played. However, if I plugged it in while the mustang splash logo (F-150 in your case) was up it worked perfectly. The call screen worked Everytime after switching cables and engaging it the first time. Text read perfectly as long as I didn't wait to plug the phone in. I don't know if it's truly the phone or is it sync itself, which as we know is not the most stable system. I can't tell you how many times my screens gone black and I had to turn the car off for 15 minutes for it to come back. Now you add Android Auto which has been quite buggy and who knows what's going on.
Anyway, if you're using a 3rd party cable try and swap it out with the Huawei one and see if that helps. Maybe also try plugging in before the splash screen goes away.