There is this weird rock explosion high up on the wall next to the ogre spawn area at the end of the Savathun strike, that I've only seen happen once. It was during a playlist run (not manually loading it up) and I've never been able to re-create the events to make it happen again. I've ruled out it being a spawn door, because it's too high up on the wall, and there doesn't seem to be any reason for it to blow open that high up, plus I don't think the spawn doors blow open on that strike anyway.