Hmm...sorry you've been having issues with it. I too have a 2017 Civic and so far CarPlay has been working great on my end. The only issue I sometimes have is very rare, (i.e has happened maybe half a dozen times since I've owned the car), but every now and then the screen will go completely blank when I'm in the CarPlay section. Hitting the Climate button to bring up the climate controls, and then hitting it again to dismiss the climate controls always does the trick - in a way, it kind of refreshes the screen to get the CarPlay display to load again.
Whenever I plug in my phone, whatever audio I was last listening to (music, audiobooks, podcasts, whatever) does automatically start playing at whatever volume I left it, even if I paused the audio before disconnecting my phone. That's kind of annoying, but I always just thought it was a flaw of CarPlay's design as opposed to it simply not working right.
Have you asked your dealership to take a look at it? Also, what kind of Lightning cable are you using to connect your phone to the system?