I still think it’s your lightmap resolution…
Did some test baking… I can get those blocky shadows only from intersecting/touching faces though or low res lightmap… but as you see even with a 128 res lightmap you can get nice gardient shadows and still… but having a higher resolution lightmap solves all the problem…
Walls are modular, long ones are from 2 pieces… boxes are lifted away from the surface by + 2 mm (first ones to the right are intersecting by 2 mm)… lit by a single HDRI… No PostProcess just exposure…