Something jammed in the rails. Inspect it I have the toyota sunroof and it slides all the way you can even tilt it more at full slide. Sometimes it would get stuck for no reason tho but once you push the button again or hold it for 2 seconds it'll move.
Mine got stuck halfway when trying to auto open it with the 2 second hold and press mode. Had to push it a couple more times but works everytime. Happens on occasion pretty strange.