Car is lowered? That would explain the camber readings.... I installed Steeda minimum drop springs and my readings were just a couple tenths of a degree less than that front and back, no camber bolts/plates required.
Screen shot of the area to activate AE in the PCM was posted just a few posts ago....
https://www.mustang6g.com/forums/threads/2018-active-exhaust-install-guide.101913/page-63#post-4515438
Requires PCM programming change (tune) to activate feature and not all Mustangs have the correct wiring/relays/fuse in place to add a kit to.
https://www.mustang6g.com/forums/threads/2018-active-exhaust-install-guide.101913
I would start by making sure both valves are actually moving. You should be able to change back and forth from quiet mode and see them fully opened and fully closed.
There is a recalibration procedure that might help...
You will need only one of the jr3z14a411j harnesses if the original is still not on your car, it is what splits from the one connector to the two harnesses that feed the actuators.
Possibly could be three harnesses missing, actuators, and mufflers needed. If you buy stock OEM pieces it is going to be pricey, Mach 1 kit + harnesses is probably your best bet. Aftermarket mufflers will probably be cheaper than stock.
Lot's of info here...