How to alter and debug views queries?
We can alter a views query using hook_views_query_alter. Try to search in your codebase for this string views_query_alter, you should get a function in one of the custom module which is implementing hook_views_query_alter.

If it doesn't help, try to enable query log using devel module, so you will know what query are being executed for that page. Views also gives the sql query that a particular display will run. See if these two sql queries don't match. You can see the diff and then try to figure out which module might be adding the additional conditions to that query.