Deploying to Heroku from Gitlab, React application w/ express server results in blank page with console logging "unexpected token" in chunk

Question

Following this tutorial to connect mailchimp api to a landing page, and skipped ahead a couple videos to deploy to Heroku https://www.youtube.com/watch?v=e0X76akgnCY&list=PLkXKwwlw4AdPUJxIkVEepQJC42TRtJ9CA&index=15&ab_channel=CodingFromNull

Able to get it to connect to and update Mailchimp list via api with local server.

The only difference is that my repository is also released at the client level on github pages, could that be the issue?

It builds successfully but then a blank page with the following errors:

Uncaught SyntaxError: Unexpected token '<' 2.3c9ee627.chunk.js:1   
Uncaught SyntaxError: Unexpected token '<'  main.78840036.chunk.js:1 
Manifest: Line: 1, column: 1, Syntax error. manifest.json:1 

In my package.json at the top level

"scripts": {
    "start": "node server.js",
    "heroku-postbuild": "cd client && npm install && npm run build",
    "test": "echo \"Error: no test specified\" && exit 1"
  },

I've gone over the tutorial several times and am stuck.

I've also tried changing heroku-postBuild to include npm start, no change in issue.

and removed from my client level package.json the links to github pages, and the scripts associated with it (https://dev.to/yuribenjamin/how-to-deploy-react-app-in-github-pages-2a1f).