Manually Programmed VCO Calibration Issue

I am working with the ADF4377 frequency synthesizer and attempting to implement manually programmed VCO calibration by reading the VCO calibration results after the PLL locks to an 8 GHz frequency. According to the datasheet, registers REG13 and REG14 should contain the VCO calibration values (m_vco_bias, m_vco_core, and m_vco_band) after a successful lock. However, despite confirming that my SPI communication is functioning correctly and waiting for the LKDET pin to go high (indicating PLL lock) before reading these registers, I consistently read 0x00 from both REG13 and REG14. This prevents me from capturing the automatically determined VCO calibration parameters that I need to manually program for subsequent frequency changes.