Undefined array key 2 in featured image

Let me start by saying this only happens when non-admins try to upload a featured image.

When clicking on “Set featured image” the upload pop-up comes up but above it, it shows the following warnings:

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/menu.php on line 181

Warning: Undefined array key 2 in /home4/mybounder/public_html/wp-admin/includes/plugin.php on line 1941

Any idea why?