I've just created a fresh WP installation and installed X 6.1.6 (running Cornerstone 3.1.6) using a child theme.
The only other plugin I have installed is the LiteSpeed Cache plugin - caching is disabled (and I cleared it to be sure)
I have also tried clearing the X style cache.
X > Theme Options > Header > Links Text > Uppercase - has no effect - I can't turn off Uppercase
Interestingly changing the font size works, and under Typography changing Uppercase for Headings also works dynamically.
It feels like this is a bug? I will provide login details in a following private post. Would be grateful if you could take a look.
It seems like I may not be the only person affected as a forum search also yields this case: https://theme.co/apex/forum/t/menu-font-showing-in-uppercase-despite-turned-off-in-options/35158
Thanks very much