Can't set maximum UHD screen resolution when using WD19S dock
I have a Dell XPS 15 7590 laptop which when connected directly to my Lenovo UHD monitor using the HDMI port allows me to use the full 3840 x 2160 resolution. However, when I try to connect the monitor via my WD19S USB-C dock, using either HDMI or Display Port, the screen resolution is only 1920 x 1080 and the options in the Display Settings control panel for changing the resolution or orientation are greyed out. I've tried updating the firmware on the laptop and the dock, and also installed the monitor driver from Lenovo. What's the solution to this problem?