It seems as though some Pixel owners are having trouble pairing their phones with their vehicles via Bluetooth, though the reports claim there are different problems in different vehicles. Back in September devices on Nougat were experiencing Bluetooth issues, so perhaps this is an extension of that.
According to the report, some people are able to connect and stream audio, but they can’t receive calls at all. Others are able to connect but will intermittently lose their connection for no reason. Other reports say that Nexus phones on 7.1 Nougat are experiencing the same issue, which is why we suspect this is tied to the original Bluetooth problem with Nougat we reported on.
Google is aware of the issue and has begun reaching out to people who have reported through the Pixel support community.