No hot water if hot water recirculator pump is shut off
I received the Caleffi NA51249 1/2" spring-loaded check valve today and installed it this afternoon. Great news! -it fixed the cold water backflow into the hot water recirculating loop whenever pulling hot water. I tested it a few times with the pump shut off and all appears to be working as it should. So, the final fix was replacing the swing type check valve, located between the hot water recirculation pump and the cold water inlet, with a spring-loaded check valve. 

I would like to "Thank" all of you for your recommendations and assistance! Greatly appreciated and Thank you for all your help!