You should be able to see an example of this here:

Click the login link in the top right of the page and a modal window pops up. The overlay, however, won't show up. If you open the chrome developer console, or resize the window, or once the slider changes slides in the background, the overlay will show up finally.

I have no idea what could be causing this?! It's affecting other pages/plugins as well. I have a plugin on one page, Bootstrap Tour, and the tour tooltips don't show up until I open the dev console or resize the window.

Hoping someone here could tell me why this would be happening?