Supply and returns are hot but radiators are cold??

I have about a 20 year Slant Fin hot water furnace that is set up for 3 zones.... 2nd floor, 1st floor and basement. The basement has been puzzling me lately. It's working but not great. From time to time I check and the supply pipe is very hot and the return line is warm but all along the radiators is cold. It makes no sense that the water is going through the pipes starting hot, then getting cold and then returning warm. Is this even possible? Is there a solution? The other 2 zones are working perfectly.

source https://hvac-talk.com/vbb/showthread.php?2224020-Supply-and-returns-are-hot-but-radiators-are-cold&goto=newpost