XF 1.5 Strange error messages

[teletubbi]

Yesterday I got some errors I never seen before.

ErrorException: Undefined index: is_admin - library/XenForo/Visitor.php:417
Generiert durch: Unbekanntes Benutzerkonto, Gestern um 21:44 Uhr
Stapelverfolgung
#0 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Visitor.php(417): XenForo_Application::handlePhpError(8, 'Undefined index...', '/var/www/html/p...', 417, Array)
#1 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Session.php(274): XenForo_Visitor::setup(10139, Array)
#2 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Controller.php(293): XenForo_Session::startPublicSession(Object(Zend_Controller_Request_Http))
#3 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Controller.php(306): XenForo_Controller->_setupSession('Index')
#4 /var/www/html/pattayaforum.net/www/forums/library/XenForo/FrontController.php(350): XenForo_Controller->preDispatch('Index', 'XenForo_Control...')
#5 /var/www/html/pattayaforum.net/www/forums/library/XenForo/FrontController.php(134): XenForo_FrontController->dispatch(Object(XenForo_RouteMatch))
#6 /var/www/html/pattayaforum.net/www/forums/index.php(13): XenForo_FrontController->run()
#7 {main}
Benötigter Status
array(3) {
["url"] => string(101) "http://www.pattayaforum.net/forums/...-traenen-und-lks-30-tage-pattaya.33564/page-2"
["_GET"] => array(0) {
}
["_POST"] => array(0) {
}
}

And this is the one it is strange for me.

ErrorException: Undefined index: is_admin - library/XenForo/Visitor.php:417
Generiert durch: Unbekanntes Benutzerkonto, Gestern um 21:46 Uhr
Stapelverfolgung
#0 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Visitor.php(417): XenForo_Application::handlePhpError(8, 'Undefined index...', '/var/www/html/p...', 417, Array)
#1 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Session.php(274): XenForo_Visitor::setup(10139, Array)
#2 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Controller.php(293): XenForo_Session::startPublicSession(Object(Zend_Controller_Request_Http))
#3 /var/www/html/pattayaforum.net/www/forums/library/XenForo/Controller.php(306): XenForo_Controller->_setupSession('Index')
#4 /var/www/html/pattayaforum.net/www/forums/library/XenForo/FrontController.php(350): XenForo_Controller->preDispatch('Index', 'XenForo_Control...')
#5 /var/www/html/pattayaforum.net/www/forums/library/XenForo/FrontController.php(134): XenForo_FrontController->dispatch(Object(XenForo_RouteMatch))
#6 /var/www/html/pattayaforum.net/www/forums/index.php(13): XenForo_FrontController->run()
#7 {main}
Benötigter Status
array(3) {
["url"] => string(106) "http://www.pattayaforum.net/forums/.../forums/&_xfNoRedirect=1&_xfResponseType=json"
["_GET"] => array(3) {
["_xfRequestUri"] => string(8) "/forums/"
["_xfNoRedirect"] => string(1) "1"
["_xfResponseType"] => string(4) "json"
}
["_POST"] => array(0) {
}
}

Any idea?

 

[Mike]

What PHP version are you running and what opcode cache are you using?

When we've seen this before, the only thing we could connect it to was opcode cache corruption, which is something we've seen every so often with APC.

 

[teletubbi]

I am using PHP Version 5.6.14-0+deb8u1 with Zend OPcache and XCache

 

[Mike]

I don't think Xcache with 5.6 is common, so that may be related. Restarting your PHP server (web server or PHP-FPM server) may resolve it, at least temporarily.

 

[teletubbi]

This combination is running without any issue since 6 month.
The error pops up only yesterday evening for about 3 minutes.