S2716DG, A07, DP will not wake with two inputs, #3

This is also affecting me:

Lenovo ThinkPad, Windows 10, using Lenovo USB Type-C dock connected to S2716DG HDMI
Gaming PC, Windows 10, with GeForce 1080 connected to S2716DG DP

I can reliably switch to HDMI and see the ThinkPad's desktop. Switching back to DP produces a "no signal" black screen. Unless I unplug the power cord, the S2716DG doesn't recognize input on DP.