Button not visible

Hello,

We are having some overlapping text and buttons that are not visible in a module, image attached.

This module has a main menu and sub-topic menus in separate scenes. The Return to Main Menu button is on the slide master and is accessible throughout the module and is working fine. The Return to Subtopic button is not visible and can only be selected by the very top right corner sliver of white visible in the image attached.

We are using Storyline 360, latest version. This is one of two modules where we have seen this problem in the last few weeks.