Just stumbled into this problem as well. Exactly what was described. If CarPlay is not turned on the iPhone, the Apple Watch continues to take phone calls. If CarPlay is turned on via the phone, the Apple Watch no longer takes calls. Power cycling just the phone will fix the issues until CarPlay is synced again. 2018 BMW.

Confirmed still not working. I thought one of the beta versions was more reliable than the release candidate. 14.4rc is 100% unreliable. Apple needs to work with cell providers to waive the monthly fees on devices that are buggy and not working. Shame on you Apple. Don’t advertise your watches are cellular if they require users to always reboot their iPhones after exciting the vehicle to get them to work again.