Hi.Ahh but the 675 uses RF not IR, I had a 1080p sony that did IR and I did get an extender for that one it never would just black out it would just drop out of 3d when it lost sync
also the projector is right above my head
Yes, the 665/675 uses RF but that is susceptible to interference too.
Try batteries or charging, but it could be just an intermittent bad signal caused possibly by something else in the room.
Also you need to pair the glasses whilst the 3D material is being shown or it will not work.
Could also possibly be a fault in the glasses themselves of course.