That makes a lot of sense!
That is the only thing I thought of after you said that. Me sliding out on the side bolster (as I normally do).
And somehow deforming the structure that holds the 2 pieces together. Which finally gave out after so many cycles.

I am surprised that if this was the case, the thing would just not have snapped the plastic.
I do have a newer foam seat cushion installed (installed a few years ago) and not original. So it is still quite firm. And I am not a fat guy, so the seat is not crushed.
But your suspected cause is the only one that makes sense. As opposed to vibration, plastic fatigue, impact, or other less likely causes.

Nevertheless, something for everyone reading this to be aware of. That this can apparently happen with ease.
Never heard about that happening to anyone else on this or other Hummer forums. So felt the need to alert everyone.

One thing that I was not aware of, until I unscrewed the seat lever unit, is that the air bladder control is a separately powered unit.
That is why it was working while the rest of the levers were not.
When you look at it, it appears to all be one unit from the outside.

 

That explains why the torsion bar on the left side of my 2 Creeks when I get in.

 

User error> H2 Driver seat not working. Those 4 tabs on the switch housing need to be carefully separated without causing damage(overextended tabs are unable to hold/secure)! The seat switch is powered by the orange wire, when some functions operate properly and others don't>>>> First thing to do is remove the 4- T15 torx screws, to REMOVE THE SWITCH, and inspect!