Dimensions (and really any of the newer data types that were added in Rhino 8 like hatches, blocks, etc.) are not currently supported in rhino.compute. They require additional care when serializing/deserializing these data types because they contain additional references to other data types in the document. Dimensions rely on another data type (i.e. an Annotation Style) which would also have to be serialized correctly in order to work properly. This is something we’re working on fixing, but currently it’s not something that is supported.