Being that the Horizons biologicals often (although not always) share a planet with geological signals/activity, and they can also spawn on atmospheric planets, that particular combination of aspects could potentially confuse a third-party app. I'd suggest checking those worlds for whether they had a thin atmosphere with them.
As said above, game is first and foremost accurate. Anything beyond that is a prediction, and that is what the third party programs do... which at this stage is likely fairly accurate, but may be thrown off by edge case scenarios like yours. Although how rare these are, I'm not completely sure. Think I found crystalline shards near the edge of the galaxy on a thin atmo world at one point, though would need to double check bookmark on the relevant account/character to be sure.
