At the risk of boring people stupid on this subject (I confess I am already!), I have for the last week and a half been away travelling in Europe and doing an extended investigation into the CarPlay and Google Maps issues.
Whereas before this trip I had had very few issues with crashing etc. - the majority of failures were suffered by my wife (iPhone 7 vs my 2016 1st-gen iPhone SE), on this trip the crashes started happening right away with my phone as well. Can my wife's phone being plugged in on charge via the 12V port whilst MY phone is 'driving' make the system fall over . . . who knows!?
Anyway, with Google Maps running on my phone, nearly every incoming WhatsApp or iMessage, whether reviewed or not, caused CarPlay to crash, often with a temporary black screen and minutes and minutes of messing around before a reconnection was possible.
So on day 2 I threw in the towel, and started using Apple maps, and for the whole of the last week, through France, Switzerland and Italy, it has been completely faultless.
There is something about the combination of VW California MY '21, iPhone, CarPlay and Google Maps which just doesn't work. Remove Google Maps from the equation, and everything becomes stable.
So Apple Maps it is for us . . . life's too short.
PS anyway, does anyone meantime have any updated information on new software updates