Versuchen wir es mit einigen Logausgaben:
Code
		
					
				    <div id="log" style="color: white;"></div>
    <script>
        // hier die Sensoren wie bisher
        const thelog = document.getElementById('log');
        function updateSpeed() {
            thelog.innerHTML += 'start geoloc<br>';
            if (navigator.geolocation) {
                thelog.innerHTML += 'geoloc avail<br>';
                navigator.geolocation.getCurrentPosition((position) => {
                    thelog.innerHTML += 'speed=' + position.coords.speed + '<br>';
                    // console.log(position, position.coords.latitude, position.coords.longitude, position.coords.speed);
                    console.log(position.coords.latitude, position.coords.longitude);
                    // document.querySelector("#getlat").textContent = position.coords.latitude;
                    // document.querySelector("#getlng").textContent = position.coords.longitude;
                    document.querySelector("#getspeed").textContent = position.coords.speed * 3.6
                });
            } else {
                thelog.innerHTML += 'geoloc not avail<br>';
            }
        }
        updateSpeed();
        setInterval(updateSpeed, 1000);
    </script>
	
			Alles anzeigen
	Dann siehst Du unterhalb der Tabelle was passiert.