Let me explain the question more clearly. I do not understand why ShotCut would play a file out of sync. (I’ve tried two different files on two different machines using several players. Only in ShotCut are the voices out of sync.) I know there are many ways that can develop. I just don’t understand why ShotCut would introduce an offset until and unless I applied a filter. That being the case, my concern is that I don’t know if correcting the error (as you suggested) will produce a predictable result.
As for being free, ShotCut is too well developed and this is so fundamental, that I just can’t imagine there is a real problem.