Madhya Gujarat Vij Company [Mgvcl] — Record of export units do not match with Solar meter record

Address:

House Number 1, Neelkanth Avenue, Bakrol Vadtal ROad

As shown in the attached image, the daily record of meter reading shows that the difference between two days of the export unit data does not match with the difference in the record of the solar meter. For every day the export data shown is one, two, or three units lesser than shown by the solar meter. The light bill records export data and hence it is a loss of on an average 30 to 60 units of solar units per month for my house. The record is taken at the same time for both export and solar meter.
I seek an explanation for this difference.