Progressions and injuries.
If your client cannot demonstrate a competent foot tripod, and they load eccentrically too long into the tib posterior, peroneus longus, and they load too much through the arch and blow into too much arch splay (loosely/slang meaning beyond reasonable pronation limits) and perhaps they evert the calcaneus a little too much.......
If . . . . if they cannot do these things properly, soundly and in a controlled fashion during a double support (standing on 2 feet) demonstration, through a simple standing knee and hip bend . . . if they cannot control their feet in this simple skill . . . .
Then, how in the heck can they do this standing on one leg,? how are they going to do it in a lunge? or as they step forward onto the foot ?How in the world will they do it walking ?
How in the world will they do it properly, soundly, running ? Squatting? Deadlifting? jumping ? or or or or . . . .
if you are wondering why your client has problems, maybe it is because they are doing things way beyond the pay grade of their foot's (limb's) abilities, skills, endurance, strength etc. If you do the simple stuff wrong, in a cheating corrupt fashion, you a will certainly do it that way when things really matter (running, lifting, playing sports).
Sometimes you have to start at the beginning, at the starting line. If your client is having pain and problems, more load doesn;t necessarily make it right. Proper loading, progressively introduced, might however.