There is technote on the issue you are facing here if you have a techconnect contract you can view it otherwise see below.
The Regional and Language settings was configured for a country that does NOT use the comma ( , ) as a List Separator. When a Data Log Configuration CSV file is imported, this appends the , on each of the tag.
Change the Regional and Language Settings to English – United States
Import the CSV file again to the Data Log using Import Tag List Overwrite
Thank you sir I have tried your solution but it did not work for me. But I used a little trick that worked for me.The trick was that if you import datalog model tags and you see a comma after each tag then you have to click option remove all and then click add all in datalog model popup. You will get all tags without comma.