I had this issue before, and in my case discovered it was due to ABS sensor faults…I had a wire that was shorting out and causing my ABS, Stability control, and traction control to stop working (intermittently) and illuminated those warnings on the dash, and anytime those warnings were illuminated, carplay navigation would go completely wonky just as you’ve described…once I resolved my ABS sensor wiring, I never had the issue again. And since my issue was intermittent, I definitely know that was the cause bc when the dash lights weren’t on, the carplay nav worked perfectly., the second they came back on it was off the rails again.
further investigation seems CarPlay uses the cars GPS not phone. In my case I got one of those cheap Chinese ones off eBay ( that causes GPS errors if its cold) my advice to anyone who reads this - dont cheap out on the GPS module.
Yeah, I can confirm that CarPlay uses the vehicle’s GPS when it is connected. One day when it was terrible weather my car couldn’t get a GPS fix so the maps were all over the place in CarPlay, but when I unplugged my phone from my car it could get a GPS fix again but the SYNC maps were messed up still.