Did you use a prewet to condition the equipment to 38 deg C? If so, this should bring the temps up. Also, if you used a prewet, did you drain well to prevent dilution of the first developer with water from the prewet? This dilution factor can hurt a lot.

In addition, did you use the times for the First Developer in a Jobo suggested by Kodak and Fuji for their films? They do differ between company brands and with the type of process.