Import and Overwrite existing Data only 75 out of 580 records updated

Import and Overwrite existing Data only 75 out of 580 records updated

 I have been trying to use the import/overwrite to add data to my existing potentials/opportunities module and all my data is clean and exact and when I import it only updates 75 records when it should update ALL records.  I do not get any errors or anything and all compulsory fields are in my import file and data in the fields.  The is no logical reason why only 75 records are updated and not all records, can ZOHO support please help, thanks.