There was a towed sonar fish lost in one of the early expeditions, 1999 or so. Location was south of the current search box on the ridge that falls away to the west.
During Niku VI, all the AUV work was in the lagoon. The AUV did have some difficulty when it came up against some of the coral heads, but it usually just backed up and tried to go around. Walt or John Clauss would know better, but I think it always managed to come home after the mission. Maybe it had to get rescued once, I can't remember. I don't think we had any technical issues with the unit itself - burning circuit boards and the like. We were able to keep it charged with the solar powered "Gobi Pack" battery suitcases we had with us.
The lagoon is only 15 ft deep, and the AUV was operating just below the surface, so the difficulty of searching, staying out of trouble, and of recovery wasn't quite like what we're seeing on this search.
Unfortunate that it is proving so difficult.
amck