I have not used or examined this antenna, but I assume it is a trapped dipole mounted as a "V." It is very like the Comet H-422. I suspect it is the same antenna with different brand names.
First, when you adjust for 40-meters, does the 40-meter SWR behave as you would expect? This cannot be a very broad bandwidth antenna, so resonance should change rapidly as you adjust it. Describe what happens to SWR on 40 as you adjust the antenna. Is it lowest at one end of the adjustment range? Is it lowest somewhere in the middle range? Is it the same 3:1 at all adjustments? If you do not see a distinct response when you change the 40-meter adjustment, it will suggest something other than the antenna, assuming the traps have not been badly adjusted.
What kind of steel structure is below the antenna? A steel building, a steel roof, steel railing...? The manufacturer claims it is insensitive to height above ground and nearby structures. At best, that is a vague claim. It cannot be strictly true.