NOT IN not returning any results even after NOT NULL statement

"NOT IN" statement not returning any records even after adding the not null in the subquery. The sub query has 6 million records and the out query has 6 records so ideally i should get 6 million minus 6 records in the below query, but i am getting zero records, The "IN" is working and returning 6 records.

select ELEMENT_ENTRY_ID from WC_TERM_ELEMENT_ENTRY_INFO_STG  WHERE ELEMENT_ENTRY_ID NOT IN(SELECT DISTINCT ELEMENT_ENTRY_GUID FROM WC_ELEMENT_ENTRIES_D WHERE ELEMENT_ENTRY_GUID IS NOT NULL

);

Any help will be greatly appreciated.

Thanks

Amit