Hi there!
First of all, can you show me a screenshot of your plugin list? Because this can be a compatibility problem. Because, if the size of your default font is 60, it should be applied to all the game, unless you have another font that is being applied on the container (windows, sprites etc...), as I can see you have two, and your second font is set to size 26. So it will also be nice to take a look at the font plugin parameter and see what scenes, sprites or windows she is covering.
You can also try to disable some plugins you think is related to the message window or messes with font in general.
It will also be nice to see your full Menu screenshot, so I can see if it is a custom menu or not.
Bottom line, if you are using a lot of plugins, test my plugin first without anyone so we can make sure it's not a compatibility problem(or change plugin order).
Let me know the results.