Menu editor – Undefined index: post_type

I am trying to edit my main menu editor I have two notices on top of my page:

Notice: Undefined index: post_type in full path … /plugins/sitepress-multilingual-cms/inc/wp-nav-menus/class-wpml-nav-menu.php on line 589

Notice: Undefined index: post_type in full path … /plugins/sitepress-multilingual-cms/inc/wp-nav-menus/class-wpml-nav-menu.php on line 594

Can this be resolved?
I’ve contacted WPML but since the errors are gone after disabling I shoul contact NextGen, so here I am…
I’m using the enfold theme but it’s persistent also with Twenty-Sixteen.

Thanks a lot in advance, have a nice day!