I cleared all filters and only had 'FullName' in the grid and it was still empty in a portal session. However, when I was logged in
everything was visible.
I noticed that the screen's base table was "Items" and the grid was as well, but the grid was "Attached". I deleted the grid and added a new one that was detached and everything now shows up in the portal session.
Do you know why an attached grid would have visible items in a normal session but not a portal session? Kind of odd but it's working now. Thank you for the help.