What gain range were you using and what kind of cable did you use?
There is always the possibility that you got a defective unit.
A scan with both units would be interesting and might tell you if the LNA is defective: Do I Need A Filter?
Also please check if you bought the filtered or unfiltered LNA from rtl-sdr blog.
The unfiltered version will obviously not be as good. You could always try the FA filter you have in front of the LNA.