All deployments fail with 'An unknown exception has occurred' at upload phase since 13 Aug - partition .7

[CurtisTFP]

Describe the bug

Since approximately 2026-08-13 12:00 UTC, every deployment to our Static Web Apps fails during the content upload phase. StaticSitesClient reports only An unknown exception has occurred immediately after Determined default file to be: index.html. Serving of already-deployed content is unaffected.

Symptoms match #1750 (slice-level upload failures, same message, clean resources affected) but on a different partition: our apps' hostnames are on .7.azurestaticapps.net.

Evidence this is service-side, not configuration

• Fails from GitHub Actions (Azure/static-web-apps-deploy@v1, Linux) AND from the SWA CLI locally (Windows; StaticSitesClient stable 689a6c1f and latest d3c91588)
• Fails for a one-file hello-world app with no config and no API
• Fails identically on two different static web apps in the subscription (tfp-portfolio-report, tfp-swa-spike)
• Deployment token rotated multiple times, fetched fresh via az at run time - no change
• Fails to the production environment AND to a newly-named preview environment
• Subscription Enabled; no Service Health events
• Production environment now stuck in Uploading since 2026-08-14 08:22 UTC after a failed attempt

Deployment IDs for backend trace

• 3765945a-66df-4962-a0ec-e950511d7024 (2026-08-14 ~08:2x UTC, production, tfp-portfolio-report)
• b031203b-c7ce-4644-aa53-cb10f84cce3b (2026-08-14 ~09:3x UTC, direct StaticSitesClient run)

Timeline

Last successful production deployment 2026-08-11; first observed failure 2026-08-13 ~12:00 UTC; all subsequent GitHub runs fail within 14-36 seconds.

Please investigate the deployment backend for partition .7 and clear the stuck Uploading deployment on tfp-portfolio-report/default.

[anilbey]

One week has passed and this issue still persists