4K HDMI not displaying

Plugable USB-C
2 ea - Dell SE2417HG Displays
Dell XPS-13

All devices are new.

Two identical external Dell displays attached to the two HDMI ports of the docking station. Both displays currently work when either is attached to the 2K port. Neither works when attached to the4K port. The display reacts upon physical connection, but then indicates that no signal is being received. The computer does not recognize the second external display (actually the third, including the laptop display). Have updated all drivers suggested by Plugable support.