Note the first link is the official VSC repo, nothing in there should fail. Can you automate testing of every theme shipped with Code? That would seem to be a good first step.
It might also be helpful to expand your error messages more. Your audience is developers here. Even if I'm not a JSON genius I can still read an error message and try to fix things myself.
I have now added fix to strip the comments, it should work now.
The last link does not have bare minimum requirement of a background color, see FAQ point 4: https://nice.github.io/themeforge/faq/#happy-little-accident...
Thanks for reporting.