Hey there,Well... if the lump is getting smaller, it may just be having a difficult time processing the crab. Time will tell.
Also, perhaps feeding it something other than cabs in the future?
My moray eel breaths heavy when he's trying to process a big meal. Also I would try silversides. They work great and they are very filling for the eel. The only time I see my eel is when he is hungry. Otherwise he hides in his burrow.