How can a Citrix Administrator enable the ability to monitor application failures for Desktop OS machines running the Virtual Delivery Agent (VDA)?

Scenario: A Citrix Administrator is in the process of migrating the existing 7.15 LTSR Virtual Delivery Agent (VDA) machines used on premises to Citrix Cloud. The administrator has created a new manual machine catalog and Delivery Group in Citrix Cloud and pointed to the existing Device Collection in Citrix Provisioning. The administrator also restarted the VDA machines.
What could prevent the VDA machines from registering in Citrix Cloud?

A user calls the help desk to report that when launching any application from within their published desktop session, it takes a long time and the overall performance is poor.
Which Citrix Director report can a Citrix Administrator use to initiate the investigation of the issue?

In a Global Server Load Balancing (GSLB) Active/Active environment, the connection proxy is used as the site persistence method.
What is used to source the traffic when connection is proxied?

Scenario: A Citrix Administrator is in the process of migrating the existing 7.15 LTSR Virtual Delivery Agent (VDA) machines used on premises to Citrix Cloud. The administrator has created a new manual machine catalog and Delivery Group in Citrix Cloud and pointed to the existing Device Collection in Citrix Provisioning.
The administrator also restarted the VDA machines.
What could prevent the VDA machines from registering in Citrix Cloud?