Cell Styles

This problem does not appear to be linked to screen size. I have a 4k, 32 inch configured for 2560x1440 and the ribbon has plenty of unused space. I have tested by adding a custom tab with the cell style button and that displays. In preferences, Styles contains (Conditional Formatting, Format as Table and Cell Styles), but only Conditional Formatting and Format as Table are displayed. There is no 'arrow' that would allow for shifting the group to show the missing Cell Styles button. 

Are there any other suggestions that I can try to resolve this problem, I would prefer to have the ribbon function as designed and intended without adding a custom tab. Thanks