1) Typically, a DVD contains *.IFO, *.BUP and *.VOB files. Out of all these, only *.VOB file contains the actual video data. Sometimes, due to file encoding or other problems, Movavi applications do not recognize the DVD structure.
In this case, try moving the *.VOB file (and only the *.VOB file) to your hard drive, into a separate folder. Once the file is on your hard drive, try converting it again, and see if the desync persist.
Otherwise, you can check this article.
2) Sometimes, even personal DVDs have protection on them. Unfortunately, our software cannot be used to remove copy protection from personal DVDs. In this case, the files from your DVD cannot be converted.
3) It's possible that the DVD has become corrupted. If the disc sustained physical damage (like scratches and so on), or the video file is damaged, then it might not convert properly.
If the video itself plays okay on your computer, you can try recording it using Movavi Screen Recorder.