Audio Sync Issue

I recently purchased an Intensity Pro 4K. I am a television historian and archivist. One of the VHS tapes I transferred ended up having the audio transferred at a different rate that the video. They audio at the end of the video is at least 20 minutes out of sync. Why could this have happened? The other tapes I have transferred turned out fine.

Please describe what was used to do the capture and on which PC platform, elsewhere no one will guess. If it was the Media Express, it may be caused by lost frames as VHS output is very unstable...