White overlay when viewing a layer for some slides

Hello,

I'm in the process of finalizing a project that was originally built by someone else in my group. One thing that I've noticed is there an internal discrepency within the course with how layer objects are working.  For some slides, when the layer is displayed the content on the stage is being screened by a faint white transparent box. For other slides with similar functionality that box does not appear.

I have compared the slide and layer properties and I cannot see a difference between the two. In other words, everything that is checked on one, is checked on the other slide.

The only thing I can think of is that I know that this course was built with different versions of Storyline. E.g., one developer is still on Update 2, while I'm on Update 3 etc.,

Any thoughts about what may be causing this overlay to appear, so I can avoid it in the future?

Thank you,

Stephen