I have the exact same problem, it started in june. The pre history on this, is that the car was not connected to any WiFi sp apparently the navigation maps would not update to the new version that Tesla released sometimes around may. And in June the car then received a new general firmware version.
Somehow the new version was expected to find the new navigation software but failed, and gave the error that the navigation needed service.
Tesla service here in Denmark thought that the above was the issue and loaded the new navigation software onto the hardware and everything seemed to be working fine. Just until early July where Tesla once again released a new version of the firmware, and the error came back. So the car went back to Tesla service. This time they thought it might be that the old version of the navigation was on a backup partition on the SD card. So they installed the navigation software on both partitions and the navigation was back to normal.
Third time in august where Tesla once again released a new firmware, that error was back... This time they (Tesla service in Denmark) thought that i might be the SD card that was failing. So they wanted to replace the SD card.
The problem is that the car now has 100.000 km on the odometer and warranty stops at 80.000 km. So they gave me a price of 500 USD for replacing the SD card. Probably work most expensive SD card... But hey, why not, I agreed to have the card replaced, and we agreed that if this did not fix the error I should not pay anything for the repair.
I gave them my car, and got a P90DL loaner. Not bad, and after three days my 6 and 8 year old girls said that the P90DL could not make their stomach tickle any more
After the first day they had the car, they gave me a call, the error move on with the SD card, so it was not the SD card that was causing this error.
Their engineer would have further look into this and we agreed I should only pay 1 hour for the troubleshooting even though the ar had been at the shop for a couple of days at that time.
After another day at the shop, another call, the problem had been escalated to engineering in the US, they claimed they had never seen this problem before...
After 7 day they came to the conclusion that the MCU needed to be replaced at a price of 5000 USD.. I said no thanks, and asked them to fix the problem back to the state where it was when I gave them the car.
This means that every time Tesla releases new software I will have to go back to the shop in order to have them to point the MCU firmware to the navigation software...
I have a really hard time believing that the MCU have a hardware failure sine it works perfectly as long I do not update the software.
If anyone has a way to fix this outside Tesla let me know since they will charge 225 USD/hour to fix it every time they releases new software.