@Corjan-Meijerink Since 18.3 I have had the double location marker problem return when connecting the device to CarPlay - this has only been tested with wired connection. It does not matter whether I start a route on the iPhone first or on CarPlay, the double marker is seen about 60% of the time on connection with CarPlay:
Even starting a route after connection does not remove the double location marker:
Normally I have to close the app on the phone and/or disconnect and then reconnect for CarPlay. I have the app logs should you need them.