Directly after updating my iPhone 8 Plus to iOS 13 on September 20th, 2019, my contacts synced to the car, were corrupted. BMW Navigation system Professional doesn't show correct contact data any longer.
Completely disconnect the Bluetooth connection to the car and cancel the previous pairing via the settings. Then pair the mobile phone completely new with the vehicle. In the course of the pairing a query dialog appears if you want to allow the vehicle access to the guestbook and synchronize the contacts to the vehicle. Answer this dialog with "Yes". Afterwards the contacts should be displayed correctly again in the vehicle.
Incident at Apple:
The incident has been reported to Apple via feedbackassitant.apple.com on September 20th, 14:08 CEST with Incident number FB7301578: