Issues with DS-2CD2042WD-I

Hi All

I've recently purchased the DS-2CD2042WD-I and paired this with a a DS-7608NI-I2. I've noticed that at night that occasionally the image for both cameras will go black and slowly re-appear. This also triggers the motion detection recording and playing it back, I still see the issue so it's not a connection issue? The camera's work fine in the daylight. Anyone else experience issues like this and aware of a fix?

Thanks

Ken