Hi Dominik,

Can you confirm what's the table type?
If you are trying this on a Simple table - For this table type, the Fixed Header is not currently available.
So if you need this feature - can you please try to create any other table type, such as a Manual table?

Let me know if that helps and if you have any questions.

If you wish to see a Fixed (Sticky) Header feature for Simple tables in the future :

Please feel free to search on our suggestions page, 

 to see if someone may be already suggested this feature. If you can't see it, feel free to add your suggestion there,  and as more people vote, the feature will move higher on the priority list.

You can certainly follow our changeLog page if you'd like ( it is also available in the plugin dashboard), where we state any changes/new features/bug fixes during updates;

and our newsletter, so you're informed about new features, bug fixes, freebies, etc.