Symptoms
When a user clicks on a reference icon lookup from Service Portal, there is no popup shown on the page.
Cause
This is caused by PRB1068750 - Service Portal - Users lose access to Service Portal pages/widgets/instances upon activation of user criteria if Explicit Roles plugin is not enabled which should be fixed from Jakarta Patch 2 onwards.
The cause is empty user criteria records being associated to the widget.
If you experience nothing being displayed when a reference icon is clicked in the portal, or a widget is not displayed, you can check to see if there are any blank user criteria set under the Can View related list of the widget.
For example, if a user clicks on the "i" icon from a catalog item on Service Portal which is a reference to the Users table and there is no popup of displaying the user's record, then check on the Form widget's Can View related list for any blank user criteria set.
Resolution
You can dis-associate the blank user criteria set under the Can View related list under the problematic widget.