Just a guess, but as the fund is holding illiquid positions, they might be calculating NAV using pricing models in instances where recent trade data is not up-to-date. With the recent jump in interest rates, they could have revised a rate variable upward therefore lowering valuations. I doubt their floaters are resetting daily, so there still may be some price sensitivity to rates.
I looked at the price action of about 10 other floating rate funds, and found that today was a quiet day ... some up slightly, some down, many unchanged. Despite what you were told I have to believe that some kind of special distribution will be paid. It is December and the fund has apparently done this in the past.
I believe that some of the Fidelity funds took a hit on maybe Visa and Master Card debt? Both stocks were hit about 15% so maybe if they have debt, Fidelity owned some of it. Curious how SPHIX and FAGIX and this fund were hit.