Two things will cause a loss of length.
One is turtling after a hanging session that places a significant amount of stress on the ligs. When the body’s attention is given to the regressed ligaments following such a exercise there will be a loss of length because the body will interpret the condition as damage (which it is) and will apply a healing process will have 4 phases of which the last phase in that healing process is to return all tissues and structures to their genetic origin.
Two is when an extended period of time lapses without any maintenance to prevent shrinkage is allowed. Many vets will attest to a loss of length after long period of inattention. That period could be 2 years or more but nevertheless it does happen. The loss may not be great, like 1/4 to 1/2” but it will happen.
So basically if someone does not keep up with it, it will go away!