I currently have the exact same problem. I also use two laptops on that U2417H. My private one with HDMI, and my work laptop with DP. Also, on my U2417H the Auto Select is greyed out. So every time I have to switch the laptop I need to set the U2417H input manually. This is a little annoying. How can Auto Select input be activated?
I have only seen one other report of this. When only ONE video cable (either HDMI or DP) is attached to the U2417H, if you enter the U2417H Menu Input Source, is Auto Select still greyed out?
When both laptops are ON and connected to the U2417H, how does Auto Select appear?
Is MST on the Display menu turned on? If so, AutoSelect is disabled. If you turn that off you should be fine. Problem is...MST is the function that lets you daisy chain DP monitors. So you can’t have both.