ASUS USB-C monitor used to work, now it doesn't.

I used to connect my ASUS USB-C ZenScreen with much success to my MacBook Pro, 13-inch, 2017. It worked perfectly. Now, all I get is "Type-C DP NO SIGNAL." I have rebooted, I have checked the display settings.

In previous threads, the Apple support pros suggested switching to the HDMI output of an external USB hub. This answer indicates that the Apple pros don't understand two important issues.

1) The entire reason for using a USB-C monitor is that you need to carry around only one extra USB-C cable; you don't have to carry a hub, an HDMI cable, the power adapter for the monitor, and the USB cable to connect the monitor to the power adapter.

2) This USED TO WORK! Now it doesn't.

This should be Apple's new motto: "It USED to work."