This was the message I received and couldn’t access my website or the dashboard. I had to deactivate the logo switcher plugin to get access to my dashboard and site.
Warning: Cannot modify header information – headers already sent by (output started at /home/mindsmatterlv/public_html/wp-content/plugins/logo-switcher/init.php:1) in /home/mindsmatterlv/public_html/wp-includes/pluggable.php on line 1167
https://wordpress.org/plugins/logo-switcher/