Error Cannot modify header information - headers already sent by

[dmundra]

Wanting to make public this bug that is also tracked in mantis: https://mantis.ilias.de/view.php?id=28387

When navigating in the plugin we get this error in the log files

Whoops\Exception\ErrorException thrown with message "Cannot modify header information - headers already sent by (output started at /var/www/html/Services/UICore/classes/class.ilTemplate.php:636)"

Stacktrace:
#6 Whoops\Exception\ErrorException in /var/www/html/Services/UICore/classes/class.ilTemplate.php:522
#5 header in /var/www/html/Services/UICore/classes/class.ilTemplate.php:522
#4 ilTemplate:show in /var/www/html/Services/Repository/classes/class.ilRepositoryGUI.php:405
#3 ilRepositoryGUI:show in /var/www/html/Services/Repository/classes/class.ilRepositoryGUI.php:356
#2 ilRepositoryGUI:executeCommand in /var/www/html/Services/UICore/classes/class.ilCtrl.php:215
#1 ilCtrl:forwardCommand in /var/www/html/Services/UICore/classes/class.ilCtrl.php:179
#0 ilCtrl:callBaseClass in /var/www/html/ilias.php:20

I tried finding the root cause but am stumped. Any thoughts? Anything I could try? We are running on PHP 7.2.

[dmundra]

Our version of Ilias is 5.4.4 but in the bug link, the error is also reported with versions 5.4.11 and 5.4.14.

[dmundra]

Another note, this issue seems to be intermittent.