I found an error that would be unlikely to manifest except in the unusual case that a custom field has been created but not yet populated with a value in any post.
When specifying such a custom field as the "order by" field in a View, the result is an incorrect "No posts found" error. The "order by" should not affect the query result, only the ordering of the result.
As soon as I populated a post with a value in the "order by" field (Numeric Rank in my example attached) the query produced the desired result.
Languages: English (English )Chinese (Simplified) (简体中文 )
Timezone: Asia/Hong_Kong (GMT+08:00)
This is expected result, Views query posts database using wordpress class WP_Query, according to wordpress document: http://codex.wordpress.org/Class_Reference/WP_Query#Order_.26_Orderby_Parameters
'meta_value' - Note that a 'meta_key=keyname' must also be present in the query.
So if you sort view by a custom field, all result should have a value in the custom field, or it will return empty items.