i would make a GUESS with nothing to support it but experience, that your problem is a cause of the emf emitter/detector in suspect spots on an atm where slots or cams are usually placed. this is a high frequency interference pattern being projected out the front of the atm, it is not meant to scramble electronics, but detect. depending on the clock frequency of the main mcu in the cam, it is possible that the emf would interfere and cause camera to act up. either that or you forget to turn it on.
nobody has true answer for this, just speculation. usually the camera needs to be switched or go to new atm or pick a new spot for cam on atm. this is not a common problem but it does happen once in awhile with cheaper Chinese cams mostly.