Failed to setup App Service deployment: UpdateSiteSourceControl failed with 409 Status (FT401019 Git error)

Question

Hello!

I have some troubles with Azure App Service deployment.

Existing deployment does not run (but only on one specific branch). It was run successfully in August, but now nothing happens on branch commit though Azure Repos Source is still connected. I see no fresh build logs on Machine so can’t understand if there any errors.

Also I can’t set up new Azure Repos deployment in Deployment Center. I have “Failed to setup deployment (UpdateSiteSourceControl) with 409 Status (FT401019 Git error)” error message. I've attached reproducing steps:

I gave all permissions for my user and for “{Project Name} Build Service ({Org Name})” on Azure DevOps and still have the same error.

---

I have fiddler logs and permissions screen of my user (I can send privately later if needed). Azure DevOps team worked on this issue and their final response was: "Checked your log, we noticed that the API used in save change is Azure API, instead of DevOps API, so this issue is from Azure App services rather than Azure DevOps. If you need more professional support on this issue, we recommend that you can try to contact the Azure App services team from this site."

I’m completely lack of ideas what else could be checked and need help.

Thanks!