The current default for projector dcp noop interval is 120sec. The DCP idle timeout in memcached is 360s. It has been seen in heavily loaded system that noop message can come in late to projector(e.g. 25 sec before the 360s timeout) and if projector is blocked on the downstream, it cannot respond to it timely.
It would be better to lower the noop interval to 20sec to improve the chances of projector getting a noop message early.