Background from Master Slide not appearing in published version

We have a series of modules that all use the same set of Master Slides for backgrounds. In just one of the modules, the backgrounds appear when you preview the module, however, they are not visible when viewing the published version of the module. The same master slide backgrounds DO appear in all of the other modules using this template.

We have ensured that the box is checked in the properties panel to "use master slide background" and we have force re-published the module, but still have no luck. The background still appears as just a white slide.

Any ideas?