Okay, these valves are not really interchangeable, and they are directional
. Are you sure that both are installed so that the water is routed away from the HWT on both? If installed backwards, you could be redirecting water back into the HWT on one or both.
You might try the "old fashioned" bypass that requires 3 of the standard on/off valves instead of 2 of the diverter valves.
ETA: Also looking at the design online, did you buy L port or T port valves? The L-hole is 1 in to 2 out, the T hole is intended for 2 in to 1 out. They would have to be installed correctly, and facing in the correct orientation.
If you have L-port valves then one would have the inlet to the cold water in, and the other would have the "inlet" facing the outlet (hot water plumbing) line. Generally the inlet side should be the bottom of the T with an L-port valve, if this is the case with your valves, then both are installed incorrectly. The middle port should be on the cold line and the hot line for each respectively, with the T-arms going one to the tank, and one to the bypass line. Looks like you would need a longer bypass tube, but swapping the supply lines with the bypasses should do the trick.
If you have T port valves, then it is a matter of adjusting the handle to divert the T in the correct direction, but in this case the bypass should be attached to the center port (which yours is).
Easy way to tell which you have, if the valve only turns 90 degrees, it is an L-port. A T-port valve should turn a full 360 degrees allowing any port to divert to any other, or to combine all 3.
If you are a visual learner, watch this video that explains the operation of both T and L valves.