External monitor causes very high CPU usage

I have an external LG 27UD69P-W monitor connected (via HDMI) to my late 2013 MacBook Pro, which causes the CPU usage of the Mac to go extremely high (kernel_task > 400%, sometimes much higher even), with the fan running very fast. (The computer is so sluggish that even the cursor does not move smoothly, often.)

Some things I've noted:

• SMC reset doesn't help.
• Safe mode doesn't help.
• GPU usage is very low (almost zero) when monitor is connected. Is this to be expected?
• Occasionally I can connect the monitor and still have a usable computer (< 50% CPU usage) for 5 or 10 minutes, but that's it.
• Monitor works fine with another MacBook.

What could be the issue here? A troublesome kext perhaps? Any suggestions?

Update

Here's my system log for when I plug in the screen and a couple of minutes after, while the computer is running sluggish / high CPU usage. Notable are the following sorts of events:

• kernel Currently unsupported feature requested
• kernel DisplayPipe Capabilities are not supported on offline Fbs
• IOAudioStream
• IOAudioEngineUserClient
• streamFormat
• coreaudiod*
• OSCMultiMonitor
• tccd
• coreduetd*
• com.apple.AmbientDisplayAgent Invalid display 0x1b5671a5

Here's a "normal" system log for a few minutes while the monitor is not plugged in.

Solution 1:

There has been some unconfirmed reports that the NVIDA drivers that came with High Sierra are not operating correctly.

Suggestion is to get updated Drivers from NVIDA directly.

Some have suggested to change the resolution back and fore to fix the problem.

It also looks like your system is no doing Graphics switching.

Check in System Preference that the Auto Graphic switching is turned on.

Also it could be very useful to us if you copy/paste some 30-50 lines in from your Console at the time when you plug in the external monitor so we can see what is going on.

Solution 2:

In reply to your updated and extended question

There is a problem with your Boom 3D

error 18:09:59.938200 +0100 Boom 3D AUBase.cpp:804:DispatchSetProperty: ca_require: inDataSize == sizeof(UInt32) InvalidPropertyValue

That probably leads to the continuous and repeating Coreaudiod and IOAudio

I do not know how to fix it, see Boom 3D support