I believe that these rendering bugs may be fixed now in the recent 3.8.0-alpha4 version.
The black render was likely caused due to some undefined vars, but now these vars all given default values to avoid this.
And the issues causing the colorful grid and overly bright render should be fixed from a combination of the previous issue as well as fixing some places where the normal value needed normalized (and in some cases not normalized)
Let me know if you get a chance to test the examples again to see if the issues have been resolved now.