After updating to ios 13, my Carplay would maybe connect 20% of the time. I would try removing from idrive and my iPhone with no success. I'm on apple's public beta updates, and I just recently updated my phone to 13.2. After the update, I removed and re-added everything, and my Carplay now works 100% of the time. It's only been a week now, but it looks like it was something in the ios update that fixed my connection issues with Carplay. There seems like there are a lot of connection issues after upgrading to ios13, and Apple is starting to fix them.
https://beta.apple.com/sp/betaprogram/