Hi Chris, I have resizable pop-ups in my project. The scroll bar only appears if the content is getting larger than your desktop screen. The way to do this is to place the content of the pop-up layout placed in a layout grid with class col-md-12. Let me know if this works.
I've managed to track down the cause. It does not actually have anything to do with the layout grids (works fine with or without), but happened because I had set the width of the popup (not the height, mind you!) to 470 in the modeler.
So fixing the width also apparently disabled the automatic resize function. A bug, I presume...
If you want to fix the width of your pop-ups; use a CSS class.
Your suggestion did not work for my current project (though I had removed all layout grids from the pop-ups, so it was worth a try), but when I ran a test with a clean project, it did.
Must be something in the custom styling, though I haven't quite figured out what. Should be able to track it down though.