Steps to reproduce:
  1. Make a new empty project
  2. Import VRC SDK
  3. Open the Build Control Panel
  4. Right click to rotate the camera in circles for about 30 seconds (framerate dependent?), editor should freeze for a few seconds.
  5. Close the Build Control Panel, repeat step 4, should be able to spin the camera indefinitely without freezing.
More info: Based on tests, Process Monitor shows that Unity.exe reads \Assets\VRCSDK\version.txt roughly 150 times per second while editor is in focus and Build Control Panel is visible, assuming every frame. A freeze of about 2.3 seconds occurs every ~5000-8000 successful read events, 16 bytes each. Having the VRChat Settings panel, and Manage Uploaded Content panel open doesn't produce read events, and doesn't cause the freezing.
SDK Version 2018.12.04.10.25
Unity version 2017.4.15f1