In SQL Server 2012, the CONTAINSTABLE function does not return RANK

I have two identical databases in SQL Server 2005 and 2012, both with the same full-text index configuration. But when I ran CONTAINSTABLE, I received a completely different result.

select max(rank) FROM CONTAINSTABLE(Candidate, (RawCopyPasteResume), 'SQL')

When I run the above query in SQL Server 2005, the RANK value is 12. However, when I run the same query on SQL Server 2012, I receive null as RANK. Because of this, I'm receiving various results for different search terms. As a result, I was unable to obtain the desired outcome. What may be the cause?
The article I read recommended to run DBCC CHECKDB WITH DATA PURITY. Also, to set your database's compatibility level to SQL Server 2012, use the following command: ALTER DATABASE SET COMPATIBILITY LEVEL=110; to rebuild the INDEX?

I can only suggest to read this article:

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