In midsummer I saw the leaves of my Albomarginata hosta go from green with creamy-white margins to solid green leaves. Also, these new leaves appeared longer and narrower than normal. No, nutrients have no bearing on this gradual color change. This reversion to green is called viridescence and is a physiological response to warm summer nights.
Full sun tends to exacerbate the change in color and appearance of the leaves.
You could force your hosta to return to its original color by cutting it down to ground level when the leaves begin to turn green. Then new white-margined foliage will emerge and remain unchanged into the fall. However, if you perform this drastic operation too often, expect to see smaller leaves in the clump in subsequent seasons. Both of my holly trees are well-formed and always have many shining black green leaves all year long. The berry loss could have been a survival response caused by drought stress.