I've had temp probe issues on my RKL as well. Probe #3 for me. It either shows iTemp error, or fluctuates so wildly that my fan and heater are freaking out. The unit was bought brand new. I'm pretty much done dealing with it after yet another itemp error in the middle of the day while I was at work, and coming home to an overheated tank with a bunch of dead coral. I'll be buying a new controller in the next couple of weeks, but it won't be DA.
I have another RKL that showed up with the same iTemp errors. I just took the whole thing offline and stuck it in a box. Not willing to risk another dead tank. My other two controllers (not DA) have never let me down. YMMV.