How does autofit work?

Personally, I never use the autofit option to "shrink text on overflow" since it will change the size of the text. The other autofit option, resize shape to fit text, is something I also avoid because it can affect line breaks. 

Thanks for clarifying that you're using the default text options and now the upgraded project text.

Do you know if "accessible text" is enabled in the player? This option is available in the player tab even if you haven't upgraded project text. 

It's also possible the learner's using a chrome extension like Helperbird to control the text sizing and spacing.