Stutter after the first second of recording

Hi, my video doorbell 2 records video and audio fine, but when I come to review footage it stops after the 1st second, stutters and then carries on, almost like it lagged a little. I.e. someone will walk into view and it will start recording, then they'll stop after the 1st second, then they'll appear a few steps on after 2nd second? Any ideas? Thanks.