Random note duration

Thanks for taking the time to make pictures and videos, but we really need to see the project to diagnose the issue properly. Please refer to this sticky thread about how to requst help most effectively:

The notes that appear with the longer duration are of course already sounding in another voice starting at the beginning of the bar, so I think what’s happening is that the piano roll is showing you the effective duration of the note that really starts at the beginning of each bar.