i have had this problem (or a similar problem) with my ancient car stereo for ages, and i fixed it today.
in the UI, i get a brief PIN prompt, which disappears in less than a second.
same thing in bluetoothctl with pair MAC. it briefly connects, attempts to pair, and immediately fails.
hcitool fails similarly (hcitool cc MAC && hcitool auth MAC fails with Input/output error).
pair MAC and then immediate trust MAC does not help.
what DID fix it for me was forcing EDR instead of EDR+LE. if i edit /etc/bluetooth/main.conf, and set ControllerMode=bredr, then pairing works just fine. it works in the ui, in bluetoothctl pair, and hcitool auth. after pairing is complete, i can then set ControllerMode back to dual, and everything works including my car stereo and my LE devices.
my stereo is the JVC KD-T900BTS, and my phone is Xperia 10 III, and i am still on SFOS=4.4.0.72
putting my soln here because this is the thread i always find when i google it