Song is reset after a few seconds (djay Pro 2 @ Mac)

After a few hours of playing music with djay Pro 2 for Mac the following problem occurs sometimes on switching between the decks: When the song on one deck has almost ended I start the song on the other deck to get a fluent transition. A few seconds after this transition the song is reset and abruptly starts from 0:00. As mentioned this problem does not occur at every transition and we can’t find any pattern or reason.