Neo_Flash,

  It might be good to talk to your support AE.

Questions and comments:

1) Which version of Spectre are you using?
   In more recent versions of Spectre should have better accuracy

2) What errpreset are you using?
   If you are doing something that requires a lot of accuracy, for
   example, simulation of an analog/digital feedback loop, then
   tighter accuracy control may help. In the past, using the Spectre
   transient option relref=pointlocal helped me for one tough circuit

3) Try AMS Designer if you have access to it

                                           Best Regards,

                                              Sheldon