The font size of a hyperlink cannot be changed from the default size of 8. 

1- If the text object was created as part of a template 
2- If the text layout and style has been modified many times

In such cases, the modifications to the text style get accumulated in the text object, and the text object no longer responds to font size changes on hyperlinks. 

The text object is an external component, and is in the way of being replaced altogether in Web Creator's next version because this issue has not been addressed by its conceptors. 

In the mean time, there is a very simple way to fix the issue: 
- Copy-paste the text in Notepad to strip all the style commands 
- Delete the text object and create a new one 
- Copy-paste the text back from Notepad 
- Change the text style, trying to limit the changes to a minimum (it is best to avoid changing the actual font, font size, and style many times over).