Missing Field in Tab View

Missing Field in Tab View

I have added "Potential" look-up field to Puchase Order and added to the tab-view(front page) that staffs can easily view which potential the purchase for.
The "Potential" view was display fine and suddenly it disappeared from the view two days ago.
When I click into the created purchase orders, the "Potential" is still there, and it just not showing anything on the display view (whole column is blank, just has the "Potential" heading on the top)
The interesting thing is, when I printed the view, the "Potentials" showed on the printed report...
No idea how to fix it.
 
Can anybody help for this?
 
Thanks
 
Amy Lau