Can’t scroll in popup anymore

I have a serious issue with this plugin which almost makes it useless. When I click on the button to set the visibility, the popup appears, however I can no longer scroll down to see things hidden below the bottom of the lightbox. I can use firebug to make the necessary adjustments to the code, combined with zooming out of the page, to view what I need to, but as anyone can imagine it’s really annoying.

This appears to have happened for no reason, I don’t think anything was update and I don’t think the plugin was updated so I have no idea what may be the cause.

I am afraid to uninstall and reinstall in case I lose all the existing widget configuration which would take a long time to redo on a side with hundreds of pages.