You can try going to the Project Settings > Rendering > Optimizations > GBuffer Format, select “High Precision Normals”.
In the viewport, open the console with ~ or go to Output Log, and type “ssr” to change the following cvars:
r.ssr.experimentaldenoiser 1
r.ssr.quality 4
r.ssr.temporal 1
More options to enable are in the mesh editor for all the meshes involved. So, right-click a mesh, select Edit, and open the LOD0 options > Build Settings at right. Put in a check in “Use High Precision Tangent Basis” and “Use Full Precision UVs”. Increase Min Lightmap Resolution to 256 at least. and under General Settings further down…set Lightmap Resolution to the Min (from above) or higher.
Does the reflective floor material have surface imperfections, or waviness or anything to it? Or is it entirely flat and completely smooth?