the spheres "hydroelastic units" are rubber and are filled with inert gas nitrogen i believe ?
over a period of time the gas goes away and spheres shrink
so more fluid has to be pumped in to maintain trim height
eventually the spheres cannot absorb suspension movement hence the riding on skateboard effect
check all mechanical parts links/knuckles for breakage/seizing then suspect the actual units

a good pointer to is to check the actual pressure that is needed when pumping up suspension
if it is excessive suspect spheres

hope this is a reasonable explanation,not used to writing essays