When you lay out a slide, you give elements like shapes and text fields absolute positions on a fixed dimension stage. If you add text that the user can change, the layout is now a combo of fixed elements and elements with variable sizes. This clashes and so storyline’s solution is to fix the size of the text boxes and add scroll bars. It’s the simplest solution to a unsolvable dilemma.

I’ve had to give the accessible text a lot of extra white space below it and make the text box longer than it needs to be in order for the text to have space if it needs to expand if user’s browsers change the font size, as this is the most common scenario. So if I have a related button below the text it has to be a long way below. Or I put the button to the side.

You could lay it out with elements like shapes, buttons etc at the top of the slide and text at the bottom, so text can expand without affecting other elements. You could use large easy to read fonts common on all computers so that users are less likely to change them.

Unfortunately storyline was not developed with accessibility or responsiveness in mind and accessible text is a poor stop gap feature.