How to Add Excerpts to Pages in WordPress?
This problem has to be somehow fixed by Themler developers. Putting snippets at the beginning of original functions.php they work. So honestly, I have no clue what they did and made it not to work. They promised execute additional-functions.php at the beginning of functions.php. Seems they forgott to do it.
Note: There is also a functions.php file in the wp-includes folder. Don’t use that one unless you are an expert PHP coder. That is a core file and only work on core files as a last resort – or never.