Objects appearing in background for new blank slides?

Hello all,

I'm currently working on a project creating training lessons for staff on Adobe Captivate 5. On the most recent training lesson I was working on, the creation of blank slides appears to be malfunctioning. Whenever I try to insert a blank slide, it appears with objects from other slides stuck in the background. I cannot manually select or delete the objects. Thinking that it might be something to do with Master Slides, I took a look there too and the Master Slides available are all blank themselves, without any objects. Even switching the malfunctioning slides to a Master Slide setting doesn't do anything for the appearance of these objects on my blank slides. Any ideas of what could be causing this?

Thanks in advance