why hmc1035 out_x muted after long work

Hi,

I have an application using HMC1035, and some mute issue occur after some days or month work on several parts. I can see with scope, there is no signal on OUT pins, although SPI communication is working and pll is locked ! Do you believe any power_up or power_down sequence problem can break these pins, or any other explanation ?

This pair of OUT pins is send to a SY54023 through capacitors, and there is no issue with working parts.

Thanks