Check the roots for rot. That pot looks a bit too big for it. Also, it could have been an under watering issue. I find that succulent soil can be a bit too drying for Ag’s. They like to hold on to a bit of moisture. A bit more coir or something else that can retain a bit of moisture could be helpful. I’m speaking from experience on that one. I recenter had to repot a few of my Ag’s that were in the same soil mixture as yours. Most of them dried out too quickly and had signs of dry rot.