I couldn’t find any filters relating to the excerpt but assumed that a ‘the_content’ filter was causing the problem. So I created an excerpt filter to generate the excerpt from the post content and that seems to have done it:
add_filter( 'the_excerpt', 'custom_the_excerpt');
function custom_the_excerpt( $content )
{
$trimmed = wp_trim_words( $content, 30, '…' );
return $trimmed;
}
Thanks