thanks for your replies.
the thing is, when I check the wireframe, the sharp shadows edges appear exactly along the edges of the original topology - not the low poly proxy. and I’ve tested the geometry extensiively in multiple applications - it renders smoothly without any more subdivisions.
as for the material, I tested many and again, no difference to the problematic areas.
the command seems to make a change, based on what I see in the console, but no value results in any visible change. it doesn’t even restart the path tracing progress bar, so I guess it’s doesn’t do anything? unless I do something wrong.