No advice other than wait till next year.
It's classic terminal freeze damage, usually from erratic temperatures
over the winter. Fan starts to grow, then gets frozen. But this
winter, with constant cold instead of the usual up and down
rollercoaster, it may just be from staying cold so long & for whatever
reason, the terminal fan couldn't take it.
I see this more often on storeboughts from warm climates with especially
"well grown" rhizomes. In my experience, those cultivars never do adjust.
Linda Mann east TN USA zone 7