Unfortunately, it is a problem to try and run the same MileIQ account on two devices at once. Having the same account on two devices can cause quite a bit of confusion as the departures and arrivals can be in multiple places simultaneously, creating all sorts of errors.
Until we're able to support use-cases like this, please delete the MileIQ app off one of the devices (or sign out and sign in with a different email on the second device).