"Disabling" Path Tracing?

Hi, I have been working on this scene with ray tracing on, with its default raytracing values in the post processing volume. So far no problems scene looking good.

Just for the sake of curiosity (the scene has a couple of particle effects and I know they are not still supported in 4.27), I turned on Path Tracing to see how the scene might look with it (from the Viewport-Lit-Path Tracing button).

But then I tried to turn it off again by just enabling the Lit button on the viewport. The scene started to look very grainy/noisy as if Path Tracing was still on and trying to calculate samples. The only workaround for it that I found so far was to increase by a lot the number of samples per pixel in GI and reflections in the post processing volume, but performance is of course diminished.

Is there another way to go back at how the scene looked with the default raytracing values? I tried turning raytracing off and on again and migrated the scene to another project, but the problem persists.

The project is on 4.27, win 10, i7 11700 with 32 Gb ram and an rtx 2070 super.

Many thanks