'Adagio' has a solid green leaf. 'Morning Light' has a green leaf with a white mid-rib.

It's common for Miscanthus to die out in the center, although it usually takes longer than 2 years. How old was the plant when installed?

A way to delay this process is to clean out the center of the crown every time you give it a haircut. The center of a grass crown can be a real trap for leaves and other detritus. It collects in there, and holds moisture. Couple this with lack of air movement, and you have a perfect environment for rotting. When I cut back my grasses, I use a pair of 12" tweezers to methodically clean out all the gunk in there.

If the center of the crown has died out, you'll know when the grass starts to grow back in. If this is the case, and it's bad enough to detract from appearance, simply divide the plant, saving the perimeter, which is newer growth, and abandon the dead/dying center.

"'Morning Light' has a green leaf with a white mid-rib."

Add "and margin" to the end of that sentence.

Center die out can be worse after winters where the temps really yo-yo alot. Be sure to rake out the clump of any debris after cutting back. Once I've cut a miscanthus down to a few inches, I'll take a stiff metal rake and really scrape through it...it won't hurt the grass a bit.