Oops, an error occurred! Code: 201605240939366c16aa1f
This does of course not help if you don't have SSH access to the live server. The exceptions also do not follow normal error flow - which means a docker logs -f does not show it, and they will also not show up on your log server.
To fix this, overwrite the default configuration in typo3conf/AdditionalConfiguration.php:
<?php // configure default logger to log to nginx error log // so that we'll see this in graylog $GLOBALS['TYPO3_CONF_VARS']['LOG'] = [ 'writerConfiguration' => [ \TYPO3\CMS\Core\Log\LogLevel::WARNING => [ \TYPO3\CMS\Core\Log\Writer\PhpErrorLogWriter::class =>  ] ] ];
Do not try to put this into typo3conf/LocalConfiguration.php; TYPO3 will merge it with the default config, leaving you with both FileWriter and PhpErrorLogWriter. TYPO3's default configuration is defined in typo3/sysext/core/Configuration/DefaultConfiguration.php.