From the information you have provided it is very difficult to offer much sensible advice. As pbxgeek suggests, check the various epoch fields, the reason may become apparent. There are many possible reasons why a call recording length may differ from the actual length of a call, there are even some cases where it can be longer if early media is recorded. Do you set recording_follow_transfer? Check also the record_completion_cause and the RTP statistics, these can help you to build a picture of what may have happened.