Orchestrator Flashes Momentarily With An "ERR_UNEXPECTED" Error And Regains Functionality

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Why an unexpected error is thrown in the Orchestrator UI, even though the Orchestrator seems to be functioning just fine?

Issue Description:

Sometimes, in very rare scenarios, an error screen is seen while logging in to the Orchestrator UI, that seems to appear for just a few seconds and vanish by itself. If tried to capture this screen, it looks like the below:

Here are few notable points:

  • An "ERR_UNEXPECTED" error (Response code 0) is observed for the "{Orchestrator URL}/identity/windows_login_callback" call which appears to be failing intermittently in the environment
  • This error is primarily observed in the Chrome browser
  • The error is transient and disappears by itself in a bit
  • The error might not reoccur in the subsequent browser loads. However, it may still resurface if the cache is cleared and attempted to reload the page
  • The error does not hamper the Orchestrator functionality
  • There might be no significant error logging
  • The exact root cause is inconclusive and might vary from environment to environment.

Diagnosis/Troubleshooting/Resolution:

  1. Based on research, it looks like this error is caused by a combination of Windows Server not supporting Windows Authentication over HTTP2 and Chrome's handling of the protocol downgrade in combination with the authentication negotiation. Disabling HTTP2 support in Chrome or on the Windows Server may resolve the problem. Follow these steps and check if that helps in alleviating the issue: Resolving Error: ERR_UNEXPECTED (Site can't be reached) in Chrome on HTTPS

  1. At times, this error has been attributed to performance issues. Add/Modify the following key to a suitable value in the Web.Config/UiPath.Orchestrator.dll.config file - and check if that helps. The default value is 30. ( How to Set Orchestrator Idle Time Before Log Off? )

  1. Close all the browser instances and run the command "ipconfig /flushdns". Validate the behavior of the Orchestrator application now. It is also a good idea in general to check if there are any intermittent network/firewall issues and work with the internal IT/Network team to resolve the same.

  1. If the DB is cluttered with a high number of records, consider performing a DB maintenance: UiPath DB Maintenance Considerations.

  1. If the issue still persists, provide the following information for further analysis:
  1. The behavior of the Orchestrator application in a private/incognito window as well as on other browsers apart from Chrome
  2. Application event logs from the Orchestrator machine
  3. A HAR trace upon reproducing the issue.