GitHub Action stuck on "Starting workflow run..."

This is an Action that I set up yesterday, and it worked successfully several times last night.

This morning, I was onboarding a colleague onto our new CI/CD process and the action keeps getting stuck on “Starting workflow run…”.

This is my yml file:

name: Deploy frontend to staging

on:
  push:
    branches: [staging]

jobs:
  build:
    runs-on: ubuntu-18.04
    steps:
      - uses: actions/checkout@v2
      - name: Set up node.js
        uses: actions/setup-node@v2
        with:
          node-version: "14"
      - name: Build app
        run: |
          npm install
          npm run build-staging
      - name: Upload static site to S3 bucket and invalidate CloudFront cache
        env:
          AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
          AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          AWS_DEFAULT_REGION: ${{ secrets.AWS_DEFAULT_REGION }}
        run: |
          aws s3 sync ./builds/staging ${{ secrets.AWS_S3_BUCKET_STAGING }} --delete
          aws cloudfront create-invalidation --distribution-id ${{ secrets.AWS_CLOUDFRONT_DISTRIBUTION_ID_STAGING }} --paths '/*'

GitHub doesn’t seem to be having any issues with Actions - checked on https://www.githubstatus.com/.

Is there a problem with my action definition?

I have the same problem on an enterprise cloud/server. I think that this problem sometimes occurs only in an enterprise these days. I have never faced it on my personal repositories.