10.13.4 is blocking my external display

I am not sure this applies if you have a display directly connected on an adapter, but it may if it is the second display on a docking station:

DisplayLink displays are a method look for creating Un-Accelerated software display buffers in RAM, and sending them out on low-speed interfaces like USB-2.

It is also used for the second and subsequent display on many Docks, but in some cases it can barely keep up with mouse-tracking, so it can be annoying.

Look on DisplayLink web site for an up-to-date Driver. Another user had a similar complaint, and was placated after checking their site, where this notice appears:

Important Information about macOS 10.13.4 update
We have become aware that installing macOS release Version 10.13.4 will cause DisplayLink connected displays to go blank after the OS upgrade, with the current DisplayLink driver [4.1] installed. Functionality such as Ethernet and audio, where implemented, is unaffected. We have alerted Apple to this issue and are working hard to find a resolution. These features continue to work as expected in 10.13.3.In the meantime, we have a new driver [4.3] that will enable clone mode, but not mirror or extended mode displays in 10.13.4. If you require mirror or extended mode displays, we recommend that you stay on macOS 10.13.3 or earlier at this time.

from:

http://www.displaylink.com/downloads/macos

.

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attentions to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your dimply more responsive.

which model alogic docking station?

Same issue here. My display (a Delll) was working fine yesterday, then upgraded to High Sierra 10.13.4 overnight and now nothing. No arrangement tab showing on the display preferences screen and no recognition of the external display. I've tried everything Grant has recommended (below) and still no improvement. I also tried holding down the "option" key whilst in display preferences to bring up the "detect displays" button, and even clicking that did not result in the external display being recognised.

Have you resolved the issue since you posted, Dallasyankee? I'm stumped...

Thanks so much, Grant. Yes, I'm connecting via an ALOGIC docking station, so it looks like this is probably the issue. Sadly clone mode won't help me much, but I have an old Air at home that I haven't upgraded to 10.13.4 - looks like that may need to be my short term option until a fix is in place. Thanks so much - I had a good look around but didn't come across that article in my searching. Appreciate your help. Samantha