I'm not sure what causes this and it's not often but rather random. Looking thru a scope doesn't fix it, but thru binoculars, it does remove the grid, so if I'd to guess it has to do something with that. I've first noticed it before couple of months, and I was on Win 7 x64 back then, now on Win 10 x64 and 0.59 (I'm playing stable only) it happened again. My video card is GeForce 650Ti, using the latest drivers. {F33018}