I know several commanders, including myself, who have systems they have visited no longer showing as visited. This typically seems to happen with game updates. I'm aware that on a PC you can save your visited stars cache file and there are ways to recover the systems you have previously visited. However, I'm not aware of any way to do this on an Xbox. I do know that while systems I have visited don't show up as such, they do still show that I have mapped the system. My suggestion is to add a filter for mapped systems. I do realize some populated systems have mapped data even though I haven't visited them.