To describe my observations and conclusions, since I have paid some deliberate attention, enough to catch the bug in the wild, so to speak.
It happens most with high speed ships, and it happens when those ships are on a manually set autopath of multiple turns. I have not seen it for ships on auto explore or auto survey. If the ship is on a multi turn auto path and if it is off screen for an entire turn of that auto path, there is a chance that it will not display the fog-revealed tiles when you do get around to looking at that region of the map. Generally, it happens when the ship is sent off into an area of solid fog. It is a display glitch. Saving and reloading refreshes the display, which means the tiles were properly marked as "revealed" in the appropriate dataset Often, sending a subsequent explorer nearby will start filling in the display when the second explorer comes close. It looks like the second explorer has this sudden invisible magic sensor range that comes into effect. It would be a clever trick if it were done on purpose.
To my knowledge, no one has successfully duplicated the behavior from a save game because, although it may be all too frequent, it is actually quite erratic. Stardock has said they cannot produce the bug on their systems. My conclusion is they need to play more and work less.
With some luck and some practice from a career of being an escalated trouble shooting resource, I managed to actually repeat it quite reliably. The real trick was catching it on the first turn of the auto path. I even took the save file to a second machine with a separate Steam account and a second copy of GalCiv, and it did the same thing. In my career of being everybody's resource when they couldn't solve their tricky problems, intermittent issues were the worst. Many a time I would have done many an evil thing to get my hands on a repeatable symptom. I only hope this is that kind of clue, and that Stardock can make use of it. Stomp those bugs!
If you are really curious, or bored waiting for Crusades,
here is the dropbox of the files I sent to Stardock. It seems that everyone has seen the problem first hand, but if you want, why not?
