Macbook Pro 15 with external monitors freezes when launching apps

willwilson wrote:

Whenever I'm using external monitors (3 to be exact),

MacBook Pro (15-inch, 2016)

Get help with video issues on external displays connected to your Mac - Apple Support
 https://support.apple.com/en-us/HT201177

Using 4K displays, 5K displays, and Ultra HD TVs with your Mac - Apple Support
 https://support.apple.com/en-us/HT206587

Use the LG UltraFine 5K Display with your Mac https://support.apple.com/en-us/HT207448

from your EtrecheckPro—

Uninstall Symantec AV and try again. Use their official uninstaller.

Uninstall CCleaner.app

willwilson wrote:

I have something required for my work called VIP Access from Symantec and I don't think it's causing any issues.

  To trouble shoot further you can:

  Try a SafeBoot https://support.apple.com/en-us/HT201262

  Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache,  etc.  

This test will tell you if third party interference; extensions etc are not loaded in safe boot mode. 

  Test issue in another user (or guest user) account  https://support.apple.com/en-us/HT204443

  This will tell you if it a universal issue or isolated to your user/admin account.