I’m having the same problem over here. In my case I was getting the yarn error message about the hash mismatch when I would build the app for deployment to Google App Engine. I had my notebook @gabgrz/github-contributions fork listed as a dependency in the package.json file.
When I ran yarn install, yarn would add this entry in the yarn.lock file for my dependency:
Removing this entry, and executing the deployment command again made the build to be successful this time.