Messages that come up with a point of exploration like a pod drop or probe or meteorite someetimes have nothing to explore when you get to the spot and the location and message stay active. Also sometimes I have noticed that there are 2 probes in the exact same spot and you can open the panel on both but there will only be one memory device to extract. It seems like after they get to old they disappear but the message stays in place and it becomes hard to know which ones are still good to explore.
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