This sounds like a polarity, phase or room issue.
Have you tried to take the sub that arrived last and position it in the same place of the first sub and connect it to the same cables as the first sub? This will rule out if it is a hardware issue with the second sub.
If after doing the above the second sub sounds like the first one, try keeping it in the same location and using the connections you were previously using for sub 2. This will rule out if it is a room issue or a cable/polarity/phase issue.
Have you tried to take the sub that arrived last and position it in the same place of the first sub and connect it to the same cables as the first sub? This will rule out if it is a hardware issue with the second sub.
If after doing the above the second sub sounds like the first one, try keeping it in the same location and using the connections you were previously using for sub 2. This will rule out if it is a room issue or a cable/polarity/phase issue.