Custom Sidebar hangs and shows warning message

Dear Team,
it's such a handy plugin, it didn't work very well from the beginning (hanging, white space), but I could work with it, but now it's all problematic with Custom Side Bar Pro. Whenever I try to make a new sidebar, the plugin hangs and it doesn't work. Also, when I try to delete a sidebar, this is very difficult to do. Moreover: there is now a warning included in all the sidebars: Warning: Missing argument 2 for apply_filters(), called in /home/My UserName/public_html/wp-content/plugins/custom-sidebars/inc/class-custom-sidebars-visibilty.php on line 531 and defined in .... wp-includes/plugin.php on line 177.
I checked the support pages, but couldn't find anything to help me. Please be so kind as to look into this matter.... Work on the site is slowing doooooooown because of this.
Kind regards,
Josh Haijer

PS I deactivated plugins like Visual Composer and so on, didn't help. I deactivated the theme (Total) and went to a Wordpress theme to no avail.