I think this solved the issue!
I did’t put this code at wp-config.php but in function.php of my child theme.
I hadn’t come across this scale down by WP in anyother project so i guessed it was TinyPNG plugin that was responsible for it.
To be honest i consider myself an experienced user when it comes to WP and i suggest that this could be integrated into the plugin settings, because not every user is confident enough to edit php code.
Thank you very much for your help!
