Unity SSGI has reflection probe fallback.
But When inetrsection occurs, very large noise occurs.
This is because the code of the SSGI shader is something strange.
float3 R = rayDirection;
float weight = 1.0f;
float intersectionDistance = EvaluateLight_EnvIntersection(posInput.positionWS, normalWS, envLightData, envLightData.influenceShapeType, R, weight);
int index = abs(envLightData.envIndex) - 1;
float2 atlasCoords = GetReflectionAtlasCoordsCube(_CubeScaleOffset[index], R, 0);
float3 probeResult = SAMPLE_TEXTURE2D_ARRAY_LOD(_ReflectionAtlas, s_trilinear_clamp_sampler, atlasCoords, 0, 0).rgb * envLightData.rangeCompressionFactorCompensation;
This is the code for the TraceReflectionProbes section of SSGI.
They do nothing after calculating intersectionDistance.
Perhaps intersectionDistance should have been converted to miplevle and then used as a parameter for sampling.
In fact, it is used that way in other Unity shader codes.
I think there was some confusion when the person in charge left the company.
Anyway, if you want to eliminate SSGI noise as a temporary measure, raise the miplevel.
I am not the person who designed the module, so I cannot restore the exact code, but you can avoid large noise by raising the miplevel to approximately 4.