I wonder if u have saved your irradiance map and light cache map, try saving it it also reduces time and flicker a it does not calculate both for every frame,
and try for the settings:-
Image sampler-
Adaptive DMC,
Sharp Quadratic,
Color Mapping-
Linear multiply.
Irradiance map-
low,
Hp Subd-50
Int Samp-20
Show calc phase ticked
And save map.
Light Cache-
Subd-1000
Samp size-0.02
And save map.
Keep settings as simple as possible Try it dude.
Show calc phase ticked
