FL are jittering. Depending on Audio driver more ore less extreme. (FL driver works best, but still not satisfying results)
When I play the MIDI signals directly in FL the problem does not appear and everything is in sync between ...
Studio One's engine.
I work a lot with audio, but I love FLstudio. The more I can stay in it without switching back in forth between FL and Studio One the better.
If any of those can be done ...