is_front_page() not working

Hey,

I like your plugin! That is what I want. I select a cpt-page as front page and its working as expected ??

But the function is_front_page isn’t working on header.

<?php if(is_front_page() ) { ?>

//do stuff

<?php } ?>

Why is the cpt-page/post not true, if I use this function in header?

https://www.ads-software.com/plugins/cpt-on-front-page/