I don't know if this will help anyone but I found that if I do the following I can get the appradio to startup properly. This is of course after I have already paired the phone thru bluetooth, physically connected the phone to the (In my case) lightning connector, clicked OK on the warning dialog box, and I am stuck in the "Connecting...." dialog box with HDMI button. If you don't get the OK button you need to disconnect the phone and restart
1) use the Mode button to access the button (Upper right hand corner) for the radio settings
2) Under Input/Output access the smartphone settings and change Connection from digital input to bluetooth audio, you will prompted to okay the disconnection of all devices which is fine since nothing is connected. You will get a confirmation tone after clicking OK
2) switch back to digital, again another tone, no need to disconnect the phone physically
3) click the Mode button, and then click on the Apps icon in the upper left.
At this point sometimes I will see the Connecting... screen briefly but I will always get the Ignore button on the radio, and my phone will show the "Allow Appradio" dialog box. Then I proceed from there and it starts up fine.
As a habit I always kill of the Appradio and Car Media Player apps on my phone before I connect up.
Hope this helps.