Not exactly the same, but related:
"According to Waze, this is a known problem with GPS with Ford Sync 3. In some cars/applications, it manifests itself as an inaccuracy to both GPS position and actual speed derived from change in GPS position of the Ford Sync module. In others, it just shows up as an actual speed inaccuracy.
Apple CarPlay gets its actual speed information from the head unit's GPS system (I guess its one of their hardware specifications that manufacturers have to implement for CarPlay), but since Waze is the only phone-based navigation app that has a feature showing actual speed (Apple Maps and Google Maps I think do not), the problem with inaccurate speeds only manifests itself when the Speed Limit feature is enabled on Waze and Waze is connected to a Ford Sync 3 head unit with Apple CarPlay.
The native app on the phone will work fine, as will Ford Sync's direct (SDL) integration with Waze (since that integration relies on the phone's GPS for location and actual speed).
According to both Waze and Apple, there is nothing either can do to fix it, nor does Apple provide any option switches to override this information with information from the phone's GPS. Rather, both say that Ford must patch/fix/replace the Sync unit so that it delivers the correct information to Apple CarPlay, which Waze then uses and displays.
Sadly, I've had to completely disable the Speed Limit feature in Waze because the problem is that annoying in my 2018 Ford Escape. Both my Ford dealer and Sync technical support acknowledge that many Sync 3 head units have been reported to have similar issues with GPS, but as of now, there is no fix/patch/update available for it, nor would anyone speak to whether it would or could be updated with a patch (as opposed to requiring a hardware replacement). From the limited research I have done, it looks like the problems have to do with recently-changed GPS specifications to accommodate the shifting magnetic poles, and it could very well be likely that the generation of GPS hardware used in many of our cars will never be able to correctly support this function again. We'll see what they say, but as of now, there are no updates or hardware replacement options (unless I buy a replacement APIM, which isn't guaranteed to not have the same problem)."
Source: [MEDIA=reddit]waze/comments/bu8xi7[/MEDIA]
When plugged into CarPlay, WAZE gets its GPS data from the car. If it hasn't been integrated quite right, your speed info will be off. You're not the only one experiencing this problem. At this point, there is no fix.