Is your dataset large with many partitions??

• Use the DESCRIBE DETAIL command to inspect the metadata of the Unity Catalog table and the cloned table. Compare the number of partitions and other metadata details.

  DESCRIBE DETAIL <unity_catalog_table>;

  DESCRIBE DETAIL <cloned_table>;

• If the Unity Catalog table has significantly more partitions or complex metadata, this could explain the performance difference.

and 

• Compare the query plans for the Unity Catalog table and the cloned table using the EXPLAIN command:

  EXPLAIN EXTENDED SELECT * FROM <unity_catalog_table>;

  EXPLAIN EXTENDED SELECT * FROM <cloned_table>;

• Look for differences in the query plan, such as additional metadata operations or lack of partition pruning.