If the tuning voltages are too low and the PLL is being programmed correctly, it means...

1. The reference frequency is too low or more likely not there at all (= zero frequency). Since the PLL tries to tune the VCOs to some rational multiple of the reference frequency, zero times whatever the multiple is still zero. The PLL tries to tune the VCOs to zero frequency by pulling the VCO lines as low as possible. The VCOs will below the normal output frequency.

2. The VCOs are unable to tune to the required frequency with a normal tuning voltage, i.e. the VCOs are being pulled as low as possible in frequency by the PLL, but still cannot be tuned to the correct output frequency. Check the VCO frequency with a counter or spectrum analyzer, it will be too high. Could be a wrong value component around the varactor & VCO resonator.

If the tuning voltage is too high, the PLL thinks the VCO is too low in frequency and is trying to pull it up. This is usually caused by the feedback signal from the VCO to the PLL being too low in amplitude (allowing the PLL input to self-oscillate at high frequency) or too high in frequency (causing the PLL counters to miscount).