Lots of questions. When was your last eye exam? How old are you? There are many reasons to lose fixation. You could be developing an eye muscle weakness. You could have mild cataracts causing a loss of contrast which causes the sight to blend into certain backgrounds. The answer to contrast is to wear a yellow or other high contrast lens color. The one fact that seems to be important, is that the problem occurs at different stages and times. Varying color and lighting conditions can have an effect on the aging eye. Even dryness can fog out the vision long enough to lose that front sight. If you trust your eye doctor, you should talk to him/her about you vision issues.