PSS failing convergence on a SMPS model

I am working on a SMSP (switching mode power supply) model, by model I mean it is just made of analogLib, ahdlLib, and a custom Verilog-A elements.

Transient simulation shows it is stable and waveform also show periodic behavior. I am using the following Spectre version:

Version 18.1.0.169.isr2 64bit -- 12 Oct 2018

I use PSS Shooting to find the steady state. It comes close (I see convergence norms as low as 7) but fails convergence. It instructs me to reduce steadyratio which I set to 10e-3 (or 1e-2) but still fails. 

It complains about signals who are perfectly behaving periodic with the beat frequency (there is only one tone). 

Any idea what can be possibly wrong?