electron-react-boilerplate: IMPOSSIBLE to debug error while building

I have spent 6 hours on this now before reporting this… I have absolutely no way of debugging this error that happens with the build-renderer script.

ERROR in unknown: Unexpected token (454:28)
error Command failed with exit code 2.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

unknown… unexpected token… i have MILLIONS of lines of code i have to read to try to find one little error somewhere!?

Any ideas on what would cause this?