Use these general steps:
Escalate as needed. For example, if the VM startup is slow, the issue could be in the hypervisor, so you can escalate it to the hypervisor administrator. Or, if the brokering time is slow, you can escalate the issue to the XenDesktop administrator to check the load balancing on the Delivery Controller.
Troubleshooting tips: Examine unusual differences, including:
If needed, click Restart to observe the user's logon process to troubleshoot issues, such as VM Start or Brokering.