I think your diagnosis is bang on.
Overpotted, too wet, too cold (and a cruel french owner who neglects it because it just grows and never flowers!)
I sprayed peroxide on the whole thing, cleaned up the rootball and removed all potting medium repotted in a smaller pot with new medium.
Will give it another spot in my windowsill.
And someday when the sweet scent of coconut reaches my nostrils, I will be thinking about you, Clint.