How long have you had it? As far as it shrinking in size, if you havent had it too long, i wouldnt worry...Whenever i move my toads (or any leather for that matter) to a different part of the tank or another tank, they tend to get ticked off. They get used to a certain flow and adapt to how that is, and if it changes on them, they have to adapt all over again so they can hold their ground (or rock rather) and hold their angle on the lights/etc...
However, i cant be sure, but it looks like yours might be rotting at the base a little? Hard to tell from the pick....might just be part of a shed (yes, they shed), but keep an eye on it. If you can tell the base right there is noticeably deteriorating, then I'd be concerned.
Give it lots of flow and lots of light, and assuming your params are in check, it should bounce back after a couple weeks or so.