Timeout errors returned when accessing published services in the ArcGIS REST Services Directory

Description

When attempting to access a published service in the ArcGIS REST Services Directory, the process fails and returns the following error message:

Error:
Error handling service request: Wait timeout for the request exceeded.
Code: 500

In some instances, when attempting to add a published service in Portal for ArcGIS Map Viewer, the process fails and returns the following error message:

Error:
Unable to add layer. Timeout exceeded.

Cause

There are no ArcSOC processes to handle the request for the services. This issue typically occurs during the initial machine start up and affects deployments that are set to use the shared instance pool instead of the dedicated instance pool.

Solution or Workaround

1. In the Windows search bar, type services, and click the Services icon.
2. In the Services window, navigate to the ArcGIS Server service and click Restart.