Accessibilty Sizing issues

My most recent course has been created from the same template as my others, but since the update, some of my titles are resizing to 9pt from 36pt whenever accessible text is clicked. It resizes some text to 9pt also when it should be 20pt. I have checked each slide and can't see any differences between those that resize and those that do not. I have changed the settings to both expand height/fixed and this doesn't help. Can anyone suggest why this is happening and what I need to do to sort it please?

Thanks