Try this. Take a piece of paper out in the roomlight and stick it in the developer. If it turns full black in your normal time, it's an exposure problem. If not, mix up new developer. I only have experience with the regular RA4 Replenisher RT (roller transport) at room temp. I assume the difference would not present problems. How are you using the developer? Do you start it or use the replenisher or what?

From your description it sounds like bad developer, but don't take my word on it.