Notes field - text is appearing very tiny on some slides

To format the notes text, you should use the View -> Notes View. This way you can see exactly what size the text is on each slide as you page through. This is also the view to use when setting up formatting for your notes.

I have used the Notes Master view in the past, but sometimes that doesn't work correctly after publishing. So I've gone to checking each slide using the Notes Page view.

This will format and change the size for both the left had Notes tab and the Notes button that shows in the bottom right of the main player bar.

HTH