The only time I've had any of my anubus turn that quickly is when I've tried soaking them in a clorox solution (to kill of any unwanted hitch-hikers) and I had too strong a solution.
Of course given that there are a bazzilion forms of anubas, it might have something to do with this particular form. But other wise, all the problems others are talking about, I've experienced with other plants, but not anubas. As a specific example about initial die-back, I've seen where this occurs with plants that are sensitive to light levels and the sudden change is light levels cause the die-back until new leaves form and grow adjusted to the new light source. But anubas are low light plants (bright light just makes them grow faster as I understand it), so I wouldn't expect such a die-back... unless perhaps you have BRIGHT light that is too much for the anuba. But even if that was the cause, I would think it would take over a week for you to notice any such thing.