BuddyPress.org

I came across several threads dealing with this particular error, and they were all related to Elegant Themes (I was having it using Divi with Buddypress), and the only solution they came up with was replacing

<title><?php elegant_titles(); ?></title>

with

<title><?php wp_title(); ?></title>

in the header.php file.

That doesn’t entirely fix the problem, because your page titles still won’t display correctly. The problem is that Elegant Themes uses elegant_titles in place of wp_titles as a function for custom title displays for their theme(s). So the best solution (at least as far as I could figure out – not really a coder) was to go into the buddypress/bp-core/bp-core-filters.php file in the Buddypress plugin and edit this line:

add_filter( 'wp_title', 'bp_modify_page_title', 10, 3 );

to say

add_filter( 'elegant_titles', 'bp_modify_page_title', 10, 3 );

This fixes the call from the plugin so that it’s actually working with your theme, rather than having BP and WP communicate over your theme’s head. I’ve noticed quite a few people are having this particular issue, and while this fix worked for my theme (Divi), you may need to check your header.php to make sure that elegant_titles is the right function for your particular theme.