Seeing the same issue as @noire.munich - tried patch-package with your changes, but no luck. This is the error log for reference:
2:41:49 PM: Error message
2:41:49 PM: Error: In file "/opt/build/repo/api/dist/functions/graphql.js": Cannot find module '../lib/auth' from '/opt/build/repo/api/dist/functions'
2:41:49 PM:
2:41:49 PM: Plugin details
2:41:49 PM: Package: @netlify/plugin-functions-core
2:41:49 PM: Version: 2.0.10
2:41:49 PM: Repository: git+https://github.com/netlify/build.git
2:41:49 PM: npm link: https://www.npmjs.com/package/@netlify/build
2:41:49 PM: Report issues: https://github.com/netlify/build/issues
2:41:49 PM:
2:41:49 PM: Error location
2:41:49 PM: In "onPostBuild" event in "@netlify/plugin-functions-core" from core
2:41:49 PM: at /opt/buildhome/.netlify-build-nvm/versions/node/v12.16.3/lib/node_modules/@netlify/build/node_modules/resolve/lib/async.js:142:35
2:41:49 PM: at load (/opt/buildhome/.netlify-build-nvm/versions/node/v12.16.3/lib/node_modules/@netlify/build/node_modules/resolve/lib/async.js:161:43)
2:41:49 PM: at onex (/opt/buildhome/.netlify-build-nvm/versions/node/v12.16.3/lib/node_modules/@netlify/build/node_modules/resolve/lib/async.js:186:17)
2:41:49 PM: at /opt/buildhome/.netlify-build-nvm/versions/node/v12.16.3/lib/node_modules/@netlify/build/node_modules/resolve/lib/async.js:13:69
2:41:49 PM: at FSReqCallback.oncomplete (fs.js:167:21)
2:41:49 PM:
2:41:49 PM: Error properties
2:41:49 PM: { code: 'MODULE_NOT_FOUND' }
It looks like a post-build issue, when netlify is trying to deploy functions.
Update: just verified its not producing the files locally either