Thank you Stephen and David,
I'll try to explain it in better way, the problem occurred just when we shoot on Canon D5, the camera is connected through the HDMI connector to converter that convert from HDMI to SDI from the converter we stream it to another converter that convert it once more to composite so we can steam it to the viewfinder and from the SDI converter we stream it to SDI monitors, the picture on the camera LCD is cut at the moment we connect the HDMI and that is all right, the problem occurred only on D5 and on record, while pausing the picture is appear again, I think that Stephen's answer is close that the converters isn't fast enough to process such information capacity.
Nice day, Yaron.