Torsion Bars
The bar has been there? It’s ether fatigue or a fracture.
If it’s a new bar, it could be poorly made, or a fracture from being dropped or mishandled.
Scoring is an issue if not addressed. That could lead to a fracture. Then there is over stressing the bar. That will lead to failure. I had a set of bars that just simply would not hold up the car anymore. I thought it odd when the second ajustment did t hold. I re adjusted it and over night it sank down. That’s when I pointed my finger at the bars and said, “YOUR FIRED!”
A friend of mine had installed oval track bars into his Duster and tried to raise the car a bit more than what the bars were designed to do. “Snap!” During the night.
Old bars that no longer retain there adjustment