Pretty simple. If the spring pressure overcomes internal tappet leakage, it collapses the plunger in the tappet. Then the valve train loses lift. Valve train is noisy due to lash in the system until the lifter recovers and fills with oil. If the valve train loses contacts between components the lifter fills with oil trying to take up the extra clearance. Now the valve doesn't seat as the lifter is too long. Engine runs rough until the lifter bleeds the excess oil fill. Providing the the lifters don't leak down or pump up any preload will work.
Doug