The first two antennas are 'unknown quantities' but the ANT-751 should produce good results if pointed toward 30° compass. The shortest elements are at the front of the ANT-751.
Try a double re-scan.
http://www.dtv.gov/rescan.html
Consider the possibility that you may have a bad connector on the coax.
Consider the possibility that the matching transformer could be bad, especially if it's the same one used with all three antennas.