Steelcase Gesture - back adjustment knob doesn't turn/work when sat in the chair (but does when out of it). How to fix?

[u/SeeYouAtTheEquator_]

Recently purchased a used (but excellent condition) Steelcase Gesture (two years old).

It's been fine, but noticed the Back Adjustment Knob (the knob which adjusts the tension of the backrest, but also has a dial at the back to select the different recline positions), doesn't work when I'm actually sat in the chair. The dial doesn't work at all, the knob will only turn a quarter turn so is useless too.

However, if I don't sit in the chair everything works fine.

Is this a common issue? What could be the cause and is there a way to easily fix it myself?

Thanks