You may see an intermittent flicker when viewing HTML5 content on an iPad or iPhone. Due to mobile Safari browser limitations, we must redraw the canvas for certain events to occur, such as displaying slide layers. When this happens, you may see a brief flicker.
We optimized HTML5 output in Update 5 for Articulate Storyline to reduce intermittent flickering. To take advantage of the new features and fixes, download and install the latest version from the link in your product confirmation email, or get it here. Then republish your project.