Unless you start sharing your autoinstall.lst files, this will be hard to troubleshoot.
Avoid using wifi updates…
There’s no need for this… Just make sure Android Auto and/or Car Play works on your current build, then you can go straight to 3.4 from there. If AA/CP do not work, make sure to install 2.2.17xxxx first → 2016 Mustang Sync3 1.0 updated to 3.0 and no Apple Carplay! - #10 by SaNdMaN