Just guessing, but I'd say it's either sitting in water, or has had too much fertilizer, or a combination of the two.

Trimming away the flopped stalks isn't a good idea right now. As long as they are green, they are making sugar for the entire plant. It would be a better idea to tie them up. A loose couple of turns of green jute twine would be almost invisible, and help hold them more upright. Just take a couple of loops around the whole plant, snug it up intil it looks good to you, and knot it.

I tied it up and it looks good.

I have not used any fertilizer except at the initial planting. It may very well be sitting in water. I had to re-plant some plants (perennials, prairie dropseed, etc.) because my planting technique in clay was not working. Amended deep holes were just collecting water. I have changed to wide shallow saucer shape holes and mounded up plantings with much more bark fines. This seems to be working. I may need to re-plant this one. Would you suggest fall or spring for re-planting?

Spring, definitely. Fall is the wrong time to move and/or divide Miscanthus. That's the season it either starts or completes blooming, and then goes into dormancy. The chances are too great it will not have time to establish in its new spot before it goes dormant. You can get away with planting a potted Miscanthus in early fall, but moving one is far more damaging to new roots.