504 Gateway Time-out after system > settings save

Working with OC 2.0.0.1 and the Journal 2 template.
I recently renamed my admin folder and applied that to admin/config.php and vqmod/pathReplaces.php.
Then I reset all file permissions: 644 for files, 755 for folders and 444 for config.php, index.php, admin/config.php, admin/index.php and system/startup.php.

Since then, when I press the save button in System > Settings, my request eventually times out and I get the 504 Gateway Time-out message.

Does anyone have an idea, how to fix this?