create-react-app (react-scripts 4.0.1) not working with react-map-gl 6.0.3

[marc-slingshot]

I am having trouble getting react-scripts and react-map-gl working together in the production build. It works when running npm run start, but the result of npm run build gives errors.

I have a repo showing the issue here - https://github.com/marc-slingshot/create-react-app-with-react-map-gl

Downgrading to 5.2.12 works. Could this be related to mapbox-gl v2? I noticed similar (but not exact) problems on this older issue thread - #176

Steps to reproduce

1. clone this repo git clone https://github.com/marc-slingshot/create-react-app-with-react-map-gl.git
2. add mapbox API token to .env.local

REACT_APP_MAPBOX_TOKEN=<your mapbox token>

1. npm i
2. npm run build
3. npm i -g serve
4. npx serve -s build
5. open up http://localhost:5000, open up dev tools, notice errors

I get the following error:

Uncaught ReferenceError: y is not defined
    at a915e7a2-d12d-45dc-b9bc-45bf5baa8c10:1
    at a915e7a2-d12d-45dc-b9bc-45bf5baa8c10:1
    at a915e7a2-d12d-45dc-b9bc-45bf5baa8c10:1

[marc-slingshot]

hrm.... looks like it's mapbox-gl upstream then according to this other open issue - #1266 and mapbox/mapbox-gl-js#10173

[Pessimistress]

Duplicate of #1266