External Monitors Switch Randomly On And Off Over and Over and Over and Over ...

Using a MacBook Pro (2018) running Mojave 10.14.6.

I have two external monitors connected - one via HDMI via a little "Dock" hub, the other directly via an HDMI-to-USB-C connector.

Every once in a while, the monitors will start randomly blinking on and off, as if they're looping through setting up the display over and over and over. Sometimes it happens once or twice, and clears up. Others, it gets into an endless loop, making it impossible to do much of anything. Rebooting sometimes helps, but not always.

Any idea what's going on here?