can you try to modify your calculation to relfect this; concat("com.google://route?saddr=", ${start_lat}, "," ,${start_lon}, "&daddr=", ${latitude}, ",", ${longitude}, "&directionsmode=", ${mode})
Remember to create starting location gps point and if possible format the destination in terms of gps points. You can create additional columns to store their corresponding gps coordinates in the choices sheet. Good also if you specify the mode of transport as either vehicle, walking, cycling, transit, motorcycle, car etc