I have a model of an industrial engine that when rendering with the workbench render engine has some bad shadows. I tried many things that I figured it may have been but it did not help. I tried:
recalculating outside Normals, merging double vertices, checking for creases and marked edges etc. If anybody has any ideal it would be a great help. It does not have this problem with EEVEE. I have uploaded the file here. Only part of the engine model is left by the way in the file. I had to delete most of it to make the file small enough to upload here.
As well I have uploaded a quick render so you can clearly see the odd shadows being produced.