The algorithms for Buffer and Combine commands can yield self-intersecting polygons when processing data. Oracle does not consider these objects valid. It will not be able to return these objects to MapInfo Pro or process them in any way.
If you must upload, store, retrieve, or otherwise use this data in Oracle, you can either find the self-intersecting polygons in the data and remove them.
To determine if your data contains self-intersecting polygons, run the table using the Check Regions command located on the SPATIAL tab and in the Objects group. To remove unwanted self-intersecting polygons, run a Clean Objects command on the table. Note that Check Regions and Clean Objects take some time to process large tables.