ISSUEThe userProfileLookup runtime function for Nintex Forms for Office 365 does not return any value
The User Profile Service may be using a different property name from the user property name being queried. Check the User Profile Service user property name by navigating to the SharePoint Admin center within Office 365 and click on User Profiles from the left menu, then click on Manage User Properties. Edit the property name and you will see under property settings a "Name" and "Display Name" field, make sure to use the "Name" field when performing the query. To get the "Name" of a user for example, use the syntax as shown below.
The below syntax will not return any result.
If the Current User is hard-coded with a value, make sure it has double quotes.
Make sure that there is no other rules that corrupted or has invalid formula.