I thought that in V18 the preview render for SSS was fixed... but I usually have to render to file to see the results. I guess keep away from GI(A:M has GI???- I think you mean Global Ambiance...) SSS needs to be traditionally 'lit' with lights to generate it's effect... to that end- some people will place a light BEHIND the SSS object(I use this light on a light-list so it does not blow-out my scene) to 'punch-up' and 'CONTROL' the SSS effect. F'R instance... if you wanted to make a waxy candle with an SSS effect at the top being generated (in effect) by the fire- you would want to place a light behind the candle toward the top... the light would help to control the amount of the SSS effect combined with the wax-group's SSS settings.
My project for this SSS candle is here on the forum somewhere... I think. This render utilized SSS, DOF, GLOW, particles, volumetric light and Jenpy's FASTAO.