I think a fast fix would be to simply remove the file /assets/snippets/reflect/snippet.reflect.php, It shouldn’t affect your usage of the Reflect snippet.
It contains the code for pasting into a snippet, and is not meant for being run on it’s own.
The reason this hack works it the following two lines:
$reflect_base = isset($reflect_base) ? $modx->config['base_path'].$reflect_base : $modx->config['base_path']."assets/snippets/reflect/";
...SNIP...
require($reflect_base."configs/default.config.php");
Since this file is called directly, $modx is not set, and hence $modx->config[’base_path’] is an empty string, and $reflect_base is just $reflect_base. So whatever file is given as argument is loaded.