I keep losing scanner range. I usually build some dedicated scanner ships (cargo hull, one small engine then loads of mk4 Scanner modules) and park them aroud the map on guard. At this point i have no "fog" and can see all about.
Then as I build and launch new ships (for example: a constructor) the view of the area defaults to that of the ships and planets which dont have scanners and the galaxy is in fog again. If I click on one of the scanner ships the real scanner depth comes straight back.
A few turns later a new ship is built and the process starts again.
EDIT: Sorry, this was supposed to appear in bug list.