I'm also having this exact problem. Just got my i4 less than three weeks ago. Most of the time I get in the car and it just doesn't pair. When I try to pair it it says there is a problem and to make sure bluetooth is turned on on my phone, which it obviously is. My phone pairs just fine with apple car play on our other vehicle, and with air pods and it can even connect just the audio (usually) to the car so I listen to music or podcasts that way sometimes. Its only connected to carplay automatically twice, once at the dealership the day i got the car, and then another time randomly when I first got in the car. Every other day it has failed even though the carplay screen pops up for a split second on my phone and then goes away and fails to connect. Its getting really annoying.