Kurouzu cancels/gets cancelled by Shingen no Ichigeki, the Gura mele punch, when there is no reason for that to be the case. We have seen blackbeard activate both fruit powers at the same time, so thats clearly not an issue.
Would make more sense if you used Kurouzu with your offhand, that way you can keep the other move activated at the same time to then hit people as they get close.
Also worth bringing up that it used to work at the same time but got changed for some reason, yet Kurouzu stays activated with other moves such as Shigan or Hakai Ho when they are basically the same.