You can demagnetize ferrite if you bang it around enough. It could have been dropped too much when being shipped. All a magnetizer does is realign the molecules to all face the correct direction. If it is thrown around or dropped too much, it would random out the alignment of the molecules in the ferrite. I would blame Fedex before TC unless it came straight from the factory demagnetized.
It doesn't happen often but it does happen. I have "banged" smaller magnets to where they lose their pull but I've never seen it done with a big subwoofer motor.