Pull fuse #32 here to reset the sync module, this always fixes these weird problems for me.
(Fuse box in the passenger kick panel)
http://www.autogenius.info/wp-content/uploads/2015/09/Ford-mustang-2015-fuse-box-passenger-compartment.jpg
Hopefully this link works, it's #32 on this diagram: ( fuse box in the passenger kick panel)
http://www.autogenius.info/wp-content/uploads/2015/09/Ford-mustang-2015-fuse-box-passenger-compartment.jpg
Disconnecting the battery never works for me, i think there must be some residual charge that...