Upgrade to 4.5.1 causes pop up to set to display:none

I installed the Pop Up plugin 4.4.5.4 and set up my PopUp, when I purchased the premium plugin and upgraded to 4.5.1 my pop up breaks.

The dark overlay happens, the pop up shows for a split second and then disappears. I checked the CSS and the pop up box is set to display: none.

When I revert back to the 4.4.5.4 plugin everything works again. Has anyone encountered this before?