Wtf. Went up against this thing in duel links: not only did ishizu set it with NO TRIBUTES, but she cleared the field turn after turn without it being destroyed by its own effect (she had no spells/traps to enable this btw).
Same thing happened with me, the dude set it with his stray lambs then half shut to save it, after the turn I kuriboh and survived the turn but gandora didn't go to the graveyard. Must be a weird glitch or maybe there's a ruling we don't know about
Dunno about the "no tribute" part, but if gandora was set and later flipped face-up and survived that, his effect won't send him to the graveyard. Being flipped face-up doesn't count as being summoned, thus his effect won't be triggered.