DisplayLink display connectivity has been limited on macOS releases 10.13.4, 10.13.5 and 10.13.6. This is solved from macOS 10.14 Mojave onwards and v5.x DisplayLink software. DisplayLink recommends updating 10.14 to restore multiple extended display support.

Users on High Sierra 10.13.4-10.13.6 who cannot update to 10.14, should install v4.3.1 for one extended USB display with multiple resolutions through an additional menu via Apple AirPlay.

An FAQ details how to enable Apple AirPlay with DisplayLink display for extend or mirror mode is available.

DisplayLink driver v4.3.1 is applicable to Mac OS X 10.12 and macOS 10.13 and can be found here: https://www.synaptics.com/node/2161.