Hello I have been using real dash for few years now and just recently the speedometer stopped working on me. Rpm’s still work as it should but with hours of research and diagnosis I’ve had no luck of figuring out the issue
- First thing to check is ‘Settings->Units & Values->Speed Source’ setting.
- Sometimes after your Android device has updated it will revoke the permissions to use GPS. That would affect your location on the map too.
It is set to be on and the location on maps works
Don’t know what could be wrong then, sorry 
You could try to reset the speed source by setting it to ECU → go back to dash and then set it back to GPS.