Music player does not start when pressing Play on stereo

I have a new Asus Zenfone 3 I bought back in February. I'm having issues getting my bluetooth devices to automatically start playing when paired. With all my previous phones, I can pair the device with bluetooth speakers (i.e. car stereo or portable speaker), press the **Play** button on the bluetooth device, and the phone would start playing music from the last app. This worked with a Samsung S2, LG G2, OnePlus One, and OnePlus Two. The process should be the same, in my experience. On my Asus phone, I have tried with both Vanilla Music Player (F-Droid App Store) and the Google Play Music app. I have started songs, got to my car, and have it continue playing. If it stops for whatever reason (i.e. a phone call), then I have to fiddle with the phone to get music playing again. My goal is to have my old behaviour without being forced to wipe and root it - connect to a bluetooth speaker, and use the bluetooth's controls for the music app *even if it's not currently running*. The phone is running Android 7.0, phone model number is ASUS_Z012DC