Nach wie vor habe ich keine Lösung für das Problem. Jetzt tritt es sogar bei einer neu installierten Domain (mauernutfraese-test.net) auf.
Hier mal ein Auszug an Fehlermeldungen für die Low Carb Zauber (WP Debug ist on):
[Mon May 09 15:44:14.227620 2016] [:error] [pid 48260:tid 139678485235456] [client 84.179.191.106:32506] PHP Notice: wpseo_pre_analysis_post_content Filter/Aktion ist seit Version WPSEO 3.0 <strong>veraltet</strong>! Benutze stattdessen javascript. in /var/www/web609/html/low-carb-zauber/wp-includes/functions.php on line 3658, referer: http://low-carb-zauber.de/wp-admin/updat…once=a7569eadcf
[Mon May 09 15:44:15.058346 2016] [:error] [pid 48260:tid 139678485235456] [client 84.179.191.106:32506] PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/web609/html/low-carb-zauber/wp-includes/functions.php:3658) in /var/www/web609/html/low-carb-zauber/wp-includes/pluggable.php on line 1171, referer: http://low-carb-zauber.de/wp-admin/updat…once=a7569eadcf
[Mon May 09 15:44:15.061362 2016] [:error] [pid 48260:tid 139678485235456] [client 84.179.191.106:32506] PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/web609/html/low-carb-zauber/wp-includes/functions.php:3658) in /var/www/web609/html/low-carb-zauber/wp-includes/pluggable.php on line 1171, referer: http://low-carb-zauber.de/wp-admin/updat…once=a7569eadcf
[Mon May 09 19:18:00.730778 2016] [core:error] [pid 48289:tid 139678485235456] [client 84.179.191.249:51713] Script timed out before returning headers: wp-cron.php
[Mon May 09 19:18:29.184658 2016] [:error] [pid 48289:tid 139678485235456] [client 84.179.191.249:51713] PHP Fatal error: Maximum execution time of 30 seconds exceeded in /var/www/web609/html/low-carb-zauber/wp-includes/functions.php on line 434
[Mon May 09 19:25:38.828253 2016] [core:error] [pid 48289:tid 139678560769792] [client 84.179.191.249:51910] Script timed out before returning headers: wp-cron.php, referer: http://low-carb-zauber.de/wp-admin/optio…age=updraftplus