For everybody dealing with bad spawns, they seem to count as giga class creatures, so gigas and carchars will take up their spawns even if they aren't in the same location. Kill the giga or carchar and fly to the swamp shortly after to have a decent chance at triggering a spawn. If you kill a rhynio and need another one, fly out of the swamp and avoid mountains to avoid spawning a giga or carchar and then fly back. This works best on island but works on lost island as well. Keep in mind that titanosaurs don't count as there will always be one on the map.