You've gotten no replies, so I'll offer what I know.....

Does the pot have a drainage hole? Do you know what kind of soil it is in? Is it still in the soil you bought it in (probably not the best as succulents are often sold in soil which does not drain well)?

It's often recommended that plants shown here be repotted in a faster draining soil, but I know with a donkey tail that's not easy since the leaves fall off so readily. Good to be careful not to overwater, but maybe you are still overwatering. Use a wooden skewer inserted in the soil for a while to test for dryness. If it comes out damp or has damp particles clinging, don't water. Also, when you do water, it's best to water until the water runs out the holes, then don't water again until dry.

Yes: in general plants of any kind losing older leaves in larger amounts than expected are either too dry or too wet. However soil mineral deficiencies can also have this effect.

Double post: there are also answers on the other thread. Pls. choose one thread to pursue or it gets too confusing.