One of my thoughts was that the "setup"-task in Qtractor should be priorized. So your experience seems to point into the same direction.
Another approach could be restarting the track-clip-playlist-threads whenever playback is stopped or the playhead is manually repositioned. Restarting it when playback is started or the playhead is manually repositioned would probably work, too, but it could add an audible delay I am afraid that might be bad especially when Qtractor is synchronized to other hard- or software.
One of my thoughts was that the "setup"-task in Qtractor should be priorized. So your experience seems to point into the same direction.
Another approach could be restarting the track-clip-playlist-threads whenever playback is stopped or the playhead is manually repositioned. Restarting it when playback is started or the playhead is manually repositioned would probably work, too, but it could add an audible delay I am afraid that might be bad especially when Qtractor is synchronized to other hard- or software.