Registered service instances are Service instance items that have been retrieved from the available services in the XenDesktop deployment and held in a directory in the Configuration service.

The following is a list of Service Instances per service for each controller in a XenDesktop 7.6 site :

 

ServiceType	Number of Instances per Controller
Acct	4
Admin	4
Analytics	2
Broker	11
Config	5
EnvTest	3
Hyp	4
Log	3
Monitor	7
Prov	3
Sf	3

The above can be verified using the following commands :

Get-ConfigRegisteredServiceInstance -ServiceType Acct | measure

Get-ConfigRegisteredServiceInstance -ServiceType Admin | measure

Get-ConfigRegisteredServiceInstance -ServiceType Analytics | measure

Get-ConfigRegisteredServiceInstance -ServiceType Broker | measure

Get-ConfigRegisteredServiceInstance -ServiceType Config | measure

Get-ConfigRegisteredServiceInstance -ServiceType EnvTest | measure

Get-ConfigRegisteredServiceInstance -ServiceType Hyp | measure

Get-ConfigRegisteredServiceInstance -ServiceType Log | measure

Get-ConfigRegisteredServiceInstance -ServiceType Monitor | measure

Get-ConfigRegisteredServiceInstance -ServiceType Prov | measure

Get-ConfigRegisteredServiceInstance -ServiceType Sf | measure

If the count in the output of these commands is lesser than the count mentioned in the above table, it is required to register the instances manually.
Say for example, the Count in the output of 'Get-ConfigRegisteredServiceInstance -ServiceType Monitor | measure' comes up as 2 instead of the ideal count of 7(as mentioned in the above table), we would need to run the command for registering the service instances for Monitor service : Get-MonitorServiceInstance | register-configserviceInstance

Similarly, we can run any of the below commands depending on the service that has instances missing :

Get-AcctServiceInstance | Register-ConfigserviceInstance 

Get-AdminServiceInstance | Register-ConfigserviceInstance 

Get-BrokerServiceInstance | Register-ConfigserviceInstance

Get-ConfigRegisteredServiceInstance | Register-ConfigserviceInstance

Get-ConfigServiceInstance | Register-ConfigserviceInstance

Get-EnvTestServiceInstance | Register-ConfigserviceInstance

Get-HypServiceInstance | Register-ConfigserviceInstance

Get-LogServiceInstance | Register-ConfigserviceInstance

Get-MonitorServiceInstance | Register-ConfigserviceInstance

Get-ProvServiceInstance | Register-ConfigserviceInstance

Get-SfServiceInstance | Register-ConfigserviceInstance

https://docs.citrix.com/de-de/xenapp-and-xendesktop/7-6/cds-sdk-wrapper-rho/xad-commands/citrix-configuration-admin-v2-wrapper-xd76/about_configconfigurationsnapin-xd76.html

http://support.citrix.com/article/CTX212941