lovell/sharp#2029
fiahfy/icns-convert#2

I can be fixed by changing the import order so that sharp will be imported before icns-convert.
I think the main problem is that the libraries are using different versions of sharp.

$ yarn list sharp    
yarn list v1.21.1
├─ @fiahfy/[email protected]
│  └─ [email protected]
└─ [email protected]
✨  Done in 0.14s.

After adding a resolution to the package.json to force the sharp version to be the same it works fine.

  "resolutions": {
    "**/sharp": "0.24.0"
  }