Hi swaraj ostwal,
This seems to be an issue of missing permissions. Please check the Application logs to find the errors regarding missing permissions when user tries to perform the requisite task and provide the same rights to the user.
I think you cannot fatch the data or valiation doesn't work because you didn't grant service execute permission. Here is my demo, please have a check:
This is The design page
No permission (but user in Everyone organization, which means he has visibility permission for mashups and widgets)
Grant Service Execute permission data can be loaded, Validator widget works to display the selected row name. But property cannot be read.
Grant Property read permission, all works on my sample
By the way, Here is a quick troubleshooting method:
During the Mashup run time page, press F12 then reload the page, if there is any 401 error, you can check the service, it means you don't have that permission.
Should you have any concern, please feel free to le me know.
Wish you a nice weekend.