There are 2 most probable symptoms - 

1. Customer created the master image from installing the OS without using any template and set the DDC servers to Connector3 and Connector4.Then Customer used the master image to deloy VDAs.
From the Citrix Health Assistant log,he spotted that the VDA was trying to connect to the Connector server named Connector1 and Connector2 which was never set using any way manually .

2.When launching the VDAs you will notice that the ICA session launch never completes and the connection sits on connecting screen forever. 

There are 2 solutions :- 
1.Disable/Prohibit "Enable auto update of controllers" policy setting >By default it is set to enabled - which means even if it is set to "Not configured" it will still be pushing the list of controllers.
2.Set the Resources to the right target Zone > for example - if there are VDAs provisioned on azure then make sure resources like - host connection, machine catalog are part of the correct azure zone. 

---

Problem Cause

From the CDF trace ,It was found that "Enable auto update of controllers" policy worked and Connector1,Connector2 were detected because of this policy .And ListOfDDCs settting was overwritten by the policy result.
The reason for why Connector1,Connector2 were detected is customer set the hostconnection of the zone to a different zone .
And this two factors finally leads to this issue.
🔻CDF
18326,0,2018/03/02 22:40:12:14428,872,9400,1,BrokerAgent,,0,,1,Information,"RegistrationManger.CreateWcfServiceList: Endpoint Address http://VDA:80/Citrix/VirtualDesktopAgent/IQueryAgent, Full Contract Name WsHttpBindingIQueryAgentEndpoint, Binding Citrix.Cds.Protocol.Worker.IQueryAgent",""
18346,1,2018/03/02 22:40:12:18288,872,9400,1,BrokerAgent,,0,,5,EntryExit,"FindControllers - entry",""
18347,1,2018/03/02 22:40:12:19301,872,9400,1,BrokerAgent,,0,,1,Information,"SiteDiscoveryManager.RestoreListOfDDCsListOfSids: Using Persisted data from:C:\Program Files\Citrix\PvsVm\Service\PersistedData\BrokerAgentInfo\SavedListOfDdcsSids.xml",""
18484,0,2018/03/02 22:40:12:31210,872,9400,1,BrokerAgent,,0,,5,EntryExit,"SiteDiscoveryManager.SingleSetOfListOfDdcs - entry",""
18487,0,2018/03/02 22:40:12:31322,872,9400,1,BrokerAgent,,0,,5,EntryExit,"HardCodedControllers - entry",""
18488,0,2018/03/02 22:40:12:31334,872,9400,1,BrokerAgent,,0,,5,EntryExit,"HardCodedControllers - exiting",""
18489,0,2018/03/02 22:40:12:31342,872,9400,1,BrokerAgent,,0,,1,Information,"SiteDiscoveryManager.SingleSetOfListOfDdcs - ListOfDDCs: Connector3 Connector3",""
18490,0,2018/03/02 22:40:12:31372,872,9400,1,BrokerAgent,,0,,5,EntryExit,"SiteDiscoveryManager.SingleSetOfListOfDdcs - exiting, Controllers:Connector3,Connector3",""
18491,0,2018/03/02 22:40:12:31374,872,9400,1,BrokerAgent,,0,,1,Information,"==>> FindControllers: AUTO-ListOfDDCs / ListOfSIDs",""
18492,0,2018/03/02 22:40:12:31436,872,9400,1,BrokerAgent,,0,,1,Information,"FindControllers ENUMERATE ListOfDDCs: 2, Connector1,Connector2",""
18493,0,2018/03/02 22:40:12:31565,872,9400,1,BrokerAgent,,0,,1,Information,"ProcessListOfDDCs: found hard-coded list of DDCs: 2, Connector1,Connector2",""
18601,0,2018/03/02 22:40:12:33311,872,9400,1,BrokerAgent,,0,,5,EntryExit,"VDARegistryBasedFarm.Initialize - entry",""
18602,0,2018/03/02 22:40:12:33320,872,9400,1,BrokerAgent,,0,,1,Information,"    Connector1",""
18603,0,2018/03/02 22:40:12:33320,872,9400,1,BrokerAgent,,0,,1,Information,"    Connector2",""
18604,0,2018/03/02 22:40:12:33321,872,9400,1,BrokerAgent,,0,,1,Information,"VDARegistryBasedFarm.Initialize - Found hard-coded list of SIDs:",""
18605,0,2018/03/02 22:40:12:33326,872,9400,1,BrokerAgent,,0,,1,Information,"    S-1-*******************-1103",""
18606,0,2018/03/02 22:40:12:33329,872,9400,1,BrokerAgent,,0,,1,Information,"VDARegistryBasedFarm.Initialize - Sid S-1-*******************-1103 is valid",""
18607,0,2018/03/02 22:40:12:33330,872,9400,1,BrokerAgent,,0,,1,Information,"    S-1-5-21-1903206714-3781320168-1442056012-1104",""
18608,0,2018/03/02 22:40:12:33330,872,9400,1,BrokerAgent,,0,,1,Information,"VDARegistryBasedFarm.Initialize - Sid S-1-*******************-1104 is valid",""
18624,0,2018/03/02 22:40:12:34122,872,9400,1,BrokerAgent,,0,,1,Information,"Creating controller info for 2 controllers",""
18625,0,2018/03/02 22:40:12:34123,872,9400,1,BrokerAgent,,0,,1,Information,"No endpoint pattern found, using defaults",""
18626,0,2018/03/02 22:40:12:34150,872,9400,1,BrokerAgent,,0,,1,Information,"Adding controller to list: Connector1,Connector2, http://Connector1:80/Citrix/CdsController/IRegistrar",""