Apple - How to fix mac os high sierra, freeze?

I was faced with the same dilemma, it seemed like my MacBook Pro (mid-2015) was 'freezing.' I stumbled across a the fix to it after seeing your post - you can read about it here: https://jrgarrigues.github.io/2017/11/05/high-sierra-freezing/

The gist of the linked article is this:

Reset your NVRAM and the SMC [System Management Controller]

First reset your NVRAM.
Turn off your Mac. Then turn it on and hold Command+Option+P+R while the computer is booting up. You will hear two chimes or on newer MacBook Pro models you will see the screen come on and go off twice.

Now, shut your computer down again and reset the SMC [System Management Controller].
With your Mac off, press Shift+Control+Option and then hold these keys while pressing and holding the power button for 10 seconds.

The first rule of troubleshooting, "isolate and identify." In other words, if you have added any hardware to your Mac over the years, remove it. I have seen RAM now recognized as "bad" by a new OS where it worked fine with the previous OS.

The comments about Safe Mode also apply as that disables third party additions to your computer. Hold down SHIFT while booting, when the Apple logo appears release shift. Booting takes longer in Safe Mode, let it do it's thing. If your Mac stops freezing then something you installed is broken under the new OS.

The 3rd thing I would try is one of the OS "cleaning" tools. I use Onyx (there are others, that's my favorite). Download it, and run the automation tool, then reboot your Mac.

Let us know the results by editing your question to indicate what you have tried.

I was having the same issue on High Sierra 10.13.3 after I migrated my system to an external SSD with APFS formatted as a BOOT DRIVE. Since the migration, I get lots of freeze and restart issues after an hour of usage or not waking up from sleep. After running ONYX (the latest), its been running like a charm, no issues so far after 14 hours of usage and switching between multiple applications.

• First try Running Onyx (Free download) maintenance Script if that doesn’t solve the problem, then:
• Second, go into recovery mode (Restart, then press Command R until you see the apple logo) and reinstall High Sierra, this may correct some issues with the OS.