Here's the stack trace, if anybody is interested in it:
#0 /var/forums/library/Dark/TaigaChat/Helper/Global.php(15): XenForo_Application::handlePhpError(8, 'Undefined offse...', '/var/forums/lib...', 15, Array)
#1 /var/forums/library/Dark/TaigaChat/EventListener/FrontControllerPreView.php(12)...