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With the latest update of the Google Chrome,  a new issue arose with menu display. 
In order to resolve it, check this article https://select.ticksy.com/article/11738

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How to Fix Pluggable.php File Errors in WordPress

If you are getting this type of error:

Warning: Cannot modify header information – headers already sent by (output started at /home/username/demosite/wp-content/themes/mytheme/functions.php:1035) in /home/username/demosite/wp-includes/pluggable.php on line 1179

Please, check this article in order to fix this issue:

http://www.wpbeginner.com/wp-tutorials/how-to-fix-pluggable-php-file-errors-in-wordpress/