HMC505LP4 and HMC440QS16G

I would like to receive your help in using the HMC505 (actually a combination of HMC505 and HMC440, THS4301, HMC433E).

I am designing circuits for VSAT communication. I want to have a 7 GHz signal as the output of the VCO-HMC505. The schematic of the design is shown below (the schematic is followed the typical PLL Application Circuit using HMC440QS16G on the datasheet):

(https://www.analog.com/media/en/technical-documentation/data-sheets/hmc440.pdf)

The difference is that instead of using VCO HMC398QS16G in the shematic, I used HMC505LP4 as I need 7 GHz for the output of VCO (not 14 GHz as the function of HMC398). 

Also, the REF signal (TCXO Oscillator) is 125 MHz (SiT502AI) (https://www.mouser.vn/ProductDetail/SiTime/SiT5021AI-2DE-33E-100000000X?qs=byeeYqUIh0M5MLW2w17eAg==) instead of 250 MHz REF.

The schematic is shown as below:

In my design, some components are mentioned below:

HMC433 (https://www.analog.com/media/en/technical-documentation/data-sheets/hmc433.pdf)

HMC505 (https://www.analog.com/media/en/technical-documentation/data-sheets/hmc505.pdf)

The output VCO is transferred to the input HMC440 through a divider (1/4; HMC433E) to get 1.75 GHz.

As a result. I get a 7GHz signal as the output of VCO.

However, I am dealing with an issue. The output of VCO does not lock exactly the phase at 7 GHz. I mean, when I place 1 MHz as the span of the Analyzer, it locked the phase but if I reduced the span of the Analyzer to 25 Khz, it showed that the signal is moving right to left (VCO did not lock the phase of the signal). The issue is shown in video attached below.

All parameters are designed and tested, they meet the requirements. Please help me to figure out the reasons why this happens as I could not figure out why ?.

Is there any problem when I design the circuits by integrating these abovementioned components with each other?

Thank you and best regards