The 6X ACOG has an issue when you ADS the scope. The view through the scope is blank, black, or red for a few seconds before loading in. I see this myself almost every time I use it and hear many others make the same complaint. This does not occur when using the red dot portion, only the full 6X part. Obviously this can cause you to miss your chance to take a shot or get killed because of the faulty scope.
Happens in TPP, could not replicate in FPP.
edit: Here are three clips I made tonight of this issue.