While setting up a new Page i found a bug on the X theme customizer.
In the Navbar section under Logo - Text the slider-input for Logo Letter Spacing (em) is not visible.
The same issue applies for Links - Text.
Here are images of said Issue:
This is a multisite installation with a currently not activated Theme using a child theme specialisce for this subsite.
x theme version is 5.1.1
I am not sure if this bug is fixed in newer versions. but as this multisite is under a live environment, I am hesitating to upgrade to the newest version for now.