Jaisree,
Check SAP note 1886388
1886388 - Characteristic values lost after order conversion
though below note is for transport order but just go through the same.
1921313 - Characteristic values lost in R/3 after a change in PP/DS transport order
Also cross check whether planned orders have relevant data which should be transferred to production order? For this you can refer below note if required.
1406920 - Descriptive characteristics not transferred to planned order
Let us know if it resolved your issue.
Regards
Rahul
