I have 2 HDMI displays connected to my dock, and am using a MacBook Pro 2018, running the latest version of Mojave.
Both displays work fine, until the screen saver kicks in and it shuts off. When I wiggle the mouse to wake everything up, only ONE screen will come back on usually. What’s weird is that sometimes it is one screen, and sometimes the other. (One is via Displaylink, of course, and I have the latest driver.)
I have to unplug the power from the dock and ‘reboot’ it to get both screens again.