On your relay board, the second largest-sized chip on that board marked "M7" on it is the diode. The stripe next to the "M" indicates the cathode, FWIW.With respect to your LED blinking problem I would bet that it is the driver itself (assuming it's an AC driver?) acting inappropriately. Can you provide more details on that driver?
Do your LEDs blink if you stop/start a high current appliance (e.g. a vacuum cleaner) on the same circuit?