Yes, this seems to be an issue with the latest iPhone OS that affects all contact applications that have groups in them. Unfortunately you will need to recreate your groups. If you still experience problems after that, deleting the app and reinstalling it should fix the problem - although you will lose your contact history and settings in the process. Sorry about the trouble.
Re: lost the data in groups
Yes, this seems to be an issue with the latest iPhone OS that affects all contact applications that have groups in them. Unfortunately you will need to recreate your groups. If you still experience problems after that, deleting the app and reinstalling it should fix the problem - although you will lose your contact history and settings in the process. Sorry about the trouble.