Hi Jamie,
The class you used to target for the background overlay is x-bnb-bg-overlay which is not a class that comes native with X. I am not certain how your pages were set before and how the class was added but if the purpose of this is to add an opaque background color to the background image of the sections, try using the either of these selectors:
.x-bg .x-bg-layer-lower-image
.x-bg .x-bg-layer-upper-image
However, please note that these classes will only be available when you enable the advanced option of the background setting of the sections:
Hope this helps.