Theme Customizer not working anymore

Let me start off by saying how much I hate themes that put majority of its functionality on WordPress Theme Customizer. I know it’s great, but when it stops working (and I can see from the forums that it does for a lot of people), there is literally no way to edit the theme. Not even from core files.

I’m running Newspaper theme and the theme customizer loads a blank page. The sidebar in the customizer loads fine (but unclickable) and where the live view is supposed to appear remains blank.

I’ve tried a couple of functions.php solutions but none of them work. I need to make change to the site’s header ad area and I’m stuck at this stupid problem (you’d expect an important area like header can be managed from inside wp-admin/theme settings, but no..!) -_-

Please help.