Why am I getting black blotches in shadow areas on a static mesh

In my scene there’s only a directional light and a skylight both set to moveble. I’ve never had these problems before. Does anyone know what might be causing them. The artifacts show up even when I use ‘force no pre-computed lighting’. Also, if I reimport the mesh, the artifacts don’t appear until the 'Generating Mesh Distance Fields" dialog goes away/

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