In your config/custom.config.php file make sure you have the following settings:
debug.level = All debug.error_reporting = E_ALL & !E_DEPRECATED zend.logger_level = DEBUG
The debug settings are probably already set this way. But if not, will cause runtime errors to be reported in the tmp/log/php.log file.
The zend.logger_level setting will have a lot of debug information to written to the tmp/log/si.log file.
If your problem still exists, zip these files together and attach to a message added to this thread.