I"m gonna blame this on a bug...
I notice that the "Server Available" indicator or whatever in the lower left of the Options menu is sometimes up and sometimes down... when down, if you return to your origin planet it would not be able to grab the discoveries and everything would appear as non-discovered.
On your own system, it may only save the last X discoveries, but it would need to get the data from the server to display anything older than that.
This sounds like a non-issue. Just perhaps confusing to some.
This too. If you discovered something while servers were unreachable, and then you eventually discovered X more things, your own system would need to scrap your original discovery with the intent of retrieving the data from server if you returned to that location. But if your discovery couldn't upload to the server at the time, it is lost.
Makes perfect sense. Not a big deal, just sucks that it needs to happen.