Logic Pro X System overloads?

What's the I/O Buffer setting in Preferences -> Audio -> Devices tab? If it's low (say, 128 and lower), try to increase it. Low settings = lower latency, but higher CPU load. In addition, you're using a very heavy multi-sampled orchestral library. I'm not sure how Kontakt handles the multi-sampled instruments, whether it streams them from the SSD or loads into RAM first. You could probably look at Kontakt's settings to see if any optimization could be set up (refer to Kontakt manual for that):

Finally, you may also freeze tracks in Logic, which helps to free up computing resources (when using multiple CPU/RAM hungry plugins). To make LPX display freeze buttons on tracks, right-click or Control-click on any track header and select Track Header Components -> Freeze. This will display freeze buttons on tracks:

Just an idea: how much free space does your system HD have left? If it's full up to the brim, here's your culprit. Your system disk (startup disk, from which the macOS boots up) should have at least the same amount of free space as the size of your RAM.

In addition to what was already said.... set Multithreading to "Playback tracks"

And this may hurt... With Logic not running... go to the Applications folder, single click the Logic icon, select "Get Info".

There should be a setting that will allow Logic to run in lo-res (non-retina) mode. Select and reboot the computer. Any better?

If I were you, I'd install macOS Sierra. High Sierra seems to be the culprit here.

If you used Logic 9.xx on Sierra you would have considerably more resources to play with.

El Capitan is even more efficient.

Yes, there is as much as a 10 to 12% performance hit in High Sierra, (depending on your computer) Apple's way of forcing upgrades is to limit what will run on the latest operating system, plus the new operating system and Logic are less efficient,.. so guess what? Hardware upgrade, new computer. This has been going on for some time now, Apple is a hardware company, the software is merely to sell hardware. Free operating system, sure!! Oops, now my applications don't run worth a ****.

Mike, sorry I only saw your post just now. I rolled back from High Sierra not because of Logic, but because it caused a significant decrease in performance of my Mac, overall. For instance, even after a clean install of High Sierra it was getting a "wheel of death" (aka "beachballing") just while running Safari, for no apparent reason. And my laptop isn't even that old (mid-2014). Anyway, some research online has shown that High Sierra is a highly sketchy macOS upgrade. Some even called it "Apple's Windows Vista". Not sure what they have done exactly, but I tend to think that "planned obsolescence" might have been a factor.

I have found that if you do not store any files on your desktop, it will reduce your amount of system overload errors.

I see, well it's definitely not the lack of storage space. To answer the question about Time Machine restore, this may erase the authorization for the plugins or other 3rd party software. So be careful about that, in case you choose to do a clean reinstall of macOS. I'd refer to the authorization info provided by the plugin developer before making any moves, though.

It doesn't matter where you store the files on the system HD, Remore. System overloads happen because the CPU cannot cope with the tasks and/or because RAM is full and is being constantly swapped to HDD and back.