maybe you have the wrong output connected to Reset.
4017 outputs go high, and the reset input requires a high. Remember that a 4017 starts counting at zero. When the counter is reset, the zero output goes high and stays high as long as Reset is high. After Reset goes low, the next clock edge makes the "1" output go high. So if output 8 is tied to Reset, on the 8th clock edge it will go high, reset the counter, and immediately go low. Whatever output is tied to reset makes very short pulse, much less than 1 microsecond, when it forces a reset.
ak