The requests that are not having a Site set means (Not associated to any site),, those requests are raised by Unknown users or Unregistered users or these users are NOT created in the application.
These requests will be viewed only by certain technicians which are described below.
This case will occur, When we enable Add unknown user as Unapproved Users under Admin -> Advanced Portal settings -> requesters
Then any user who is not registered in the application sends an email to the support email address configured in the SDP MSP application, they will be considered as Unknown users. These users will be listed only under a special Request filter named Unknown requests.