Hello OnTopOfTheHill.
Thank you for using Apple Support Communities. It sounds like you're experiencing a very unique issue when using CarPlay. Specifically, it's only working at specific times. We can understand how this would be an issue. Allow us to investigate this issue and assist in any way we can.
For issues using CarPlay, you'll want to follow the troubleshooting steps listed in the resource below:
If you need help with CarPlay - Apple Support
This specific resource covers all steps you can attempt for CarPlay issues. If your issue continues, you'll want to contact Apple Support using the link at the very bottom of the resource we shared with you.
We hope this information is useful. Best of luck.