Wow, that’s nasty massive. Sure does look like it needs a high pass around there. Dial in 17 or 18 Hz, maybe 19, if you can, with a very steep cutoff and try to recreate that same problem. You’ll know if you are on the right track.
That subwoofer is an underhung motor design that uses a T pole. Basically that T is hitting the front plate (aka you have hit your mechanical limits). You will want to add a steep HP filter around 20Hz to protect against that. I ran a 4th order High Pass centered on 20Hz. You could try something different. But you have two choices, either add a high pass or lower the wattage going to the subwoofer.