I am currently having this issue where 2D layers close to each other will create shadow artifacts that are unwanted, even z-tearing artifacts when no Z coordinate is the same.
Is there any solution to this? I am having the same issue where I have two planes both with masked opacity and I seem to be unable to disable the contact shadows.
There is also a setting to cast shadows on the material settings as well, try that too then look into recalculating normals and tangents in modelling mode, that sometimes fixes it too