I've been going back and re-scanning my missing systems (which were originally scanned after the problem developed), and I'm running into an occasional missing body similar to what's described in
post #829 of this thread.
For example, I see this in the navigation panel:
HIP 15937
-HIP 15937 6
--HIP 15937 6 A
--HIP 15937 6 B
--HIP 15937 6 D
Note that HIP 15937 C is missing. It shows in the system map, but as an outlined black circle, and I seem to already know about it even though I had to re-discover/scan the rest of the system. I can target it via the system map and fly to it, but its still missing from the navigation panel (and which shows no target marker).
Hm, even though its already known and won't scan, it does seem to be missing some data, such as type:
HIP 15937 6 C
Anarchy
None
(is it rocky, ice, earth-like, what?) In the system map, it says its a rocky body, but this does not show on the HUD.
I noticed this in at least one other system I've recently visited as well (though I didn't check all these details at the time).