Static Web Apps deployments failing/hanging since ~14:10 UTC on 21 July 2026 (BadRequest content server errors + upload timeouts)

**Describe the bug**

Our Static Web App has been deploying successfully via GitHub Actions (Azure/static-web-apps-deploy@v1) multiple times per hour throughout the day. The last successful deployment completed at 14:10 UTC on 21 July 2026. Every deployment attempt since then has failed, with two distinct symptoms appearing across different runs:

Immediate failure with the message:
We are currently experiencing problems communicating with our content server. Please try again later or file an issue if this behavior continues.
Upload succeeds and the deployment shows Status: InProgress, but then times out after 500+ seconds with:
Upload Timed Out. Unsure if deployment was successful or not.
A clear and concise description of what the bug is.

**To Reproduce**
We ruled out any issue on our side by deploying a completely unmodified, trivial static HTML file with no build steps and no dependencies — it hung/failed in exactly the same way as our normal app. This confirms the issue is not related to repository content, app size, or configuration.

Relevant config: app_location: /, no API directory, staticwebapp.config.json present, no database connections configured.

Expected behavior

Deployment completes successfully as it had been doing consistently prior to 14:10 UTC.

Deployment IDs for reference

69a30c78-34af-49fc-9df0-ca1f58f823e4
7f706473-f75e-4a54-a22a-d7c02e3834b7
3c4696d0-173c-4c15-9f64-8cf4447bf9fa

Review the Azure/static-web-apps-deploy@v1 workflow, app_location setting, and staticwebapp.config.json, then use the listed deployment IDs to compare the failing runs with the last successful deployment. Confirm the cause of the content-server errors or upload timeouts and verify that an unchanged static HTML deployment completes successfully.

Written by the indexing model from the issue text.