Hey Reticguy, sorry to hear you lost one. I had one with the exact symptoms and ended with the same result. I am not up on my disease terminology or exactly how bacteria grows/spreads, but one thing I noticed, and have seen since is if the substrate gets oversaturated my frogs immediately show signs of bacterial infections/fungal infection/toxing out on something (unnaturally bloated up, hip bones showing, skin looks really thin, tacky skin, retained sheds, some of them lose appetite, but not all.)

I haven't lost any other frogs, but I know it is the oversaturation. It may be do to the ability of bacteria to reproduce and easily spread in the 'standing' water in the bottom of the tank/substrate. I started making my substrate deeper and changing more often if it becomes too saturated. Ventilation is also important.