Multisite Switcher Error?

The main language on the website shows fine. If I switch to the seconde language of the page I get a blank page with the error:

Warning: preg_match() expects parameter 2 to be string, object given in /home/website/public_html/wp-includes/post-template.php on line 254

Catchable fatal error: Object of class WP_Post could not be converted to string in /home/website/public_html/wp-includes/post-template.php on line 272

The code is:

$content = $pages[$page - 1];
LINE 254	if ( preg_match( '/<!--more(.*?)?-->/', $content, $matches ) ) {
		$content = explode( $matches[0], $content, 2 );
		if ( ! empty( $matches[1] ) && ! empty( $more_link_text ) )
			$more_link_text = strip_tags( wp_kses_no_null( trim( $matches[1] ) ) );

		$has_teaser = true;
	} else {
		$content = array( $content );
	}

	if ( false !== strpos( $post->post_content, '<!--noteaser-->' ) && ( ! $multipage || $page == 1 ) )
		$strip_teaser = true;

	$teaser = $content[0];

if ( $more && $strip_teaser && $has_teaser )
		$teaser = '';

LINE 272	$output .= $teaser;

If I comment this codeblock out I don’t see the content in neither language, but all the rest is showing on both languages.

Is this a problem of the multisite language switcher?

https://ww.wp.xz.cn/plugins/multisite-language-switcher/