Radio Frequency Switch design problem
The PIN diode is not spec'd past 6GHz.

The self-inductance is 0.6nH; Zl at 10GHz is +j36 ohms.

I imagine you have some DC_blocking caps (100pF each), one on each side of the PIN diode. Also some PCB traces. At 1nH each (cap, trace, trace, cap), or 4nH total, that inductance (if pure inductance) is +j252 ohms.

Is this embedded inside a 50_ohm system? Wavelength of 10GHz is 3.3cm. Are your traces 0.1" wide above 1/16" FR4 above GND? That is 50_ohm with 1/16th" dielectric. Are the capacitors 0.1" wide, so they look (close to) 50_ohms also?

How do you get the current in (50mA, at least)? are those connections acting as tuning-stubs?

If the PIN is self-resonant at 10GHz, run it in a Network Analyzer, and use Smith Chart to define tuning stubs to detune the 10GHz problem.