I'm having a lot of trouble getting an error fixed on my Magento2 installation (version 2.2). It occurs when logging in at admin (backend) or at account login on the frontend. Please find below the entries in the log. Would anyone have a hint or clue how to solve this? Any help is highly appreciated.
Many thanks.
-U
[Mon Nov 06 04:24:18.998328 2017] [proxy_fcgi:error] [pid 30863:tid 139625581967104] [client xx.xx.xx.xx:51374] AH01071: Got error 'PHP message: PHP Fatal error: Uncaught Error: Class 'Zend\Db\Sql\Expression' not found in /var/www/webdir/html/vendor/magento/module-captcha/Model/ResourceModel/Log.php:82\nStack trace:\n#0 /var/www/webdir/html/vendor/magento/module-captcha/Model/DefaultModel.php(345): Magento\Captcha\Model\ResourceModel\Log->logAttempt('john')\n#1 /var/www/webdir/html/vendor/magento/module-captcha/Observer/CheckUserLoginBackendObserver.php(61): Magento\Captcha\Model\DefaultModel->logAttempt('john')\n#2 /var/www/webdir/html/vendor/magento/framework/Event/Invoker/InvokerDefault.php(72): Magento\Captcha\Observer\CheckUserLoginBackendObserver->execute(Object(Magento\Framework\Event\Observer))\n#3 /var/www/webdir/html/vendor/magento/framework/Event/Invoker/InvokerDefault.php(60): Magento\Framework\Event\Invoker\InvokerDefault->_callObserverMethod(Object(Magento\Captcha\Observer\CheckUserLoginBackendObserver), Object(Magento\Framework\Event\Observer))\n#4 /var/www/webdir/html/vendor/mag...\n', referer: https://www.webdir/admin/admin/index/index/key/11a9fc911e4a89d53e03d14a32dbcd76a057cfdf642ce2af4526fe4cc9339542/