My guess is you are using a huge plane so the shadow resolution is too small for sharp shadow (there is no cascade shadows in Nomad, and the fixed resolution is only 512x512).
The frame accumulate usually “smooths aways” so low resolution can allow you to have a smooth shadows, but it’s a side effect, not really a feature.
I might add smooth shadow at some point by jittering the light oriented a little bit and then let the frame accumulation do the rest of the work.