Are you able to easily uninstall/reinstall Sunflower?
Uninstall, restart Mac, then see what happens in iReal Pro—to test if Sunflower is somehow blocking our output (has it had an update recently? It could have older code). We have made changes as you know to how iReal Pro functions with audio devices and Airplay so there might be something we need to check further. We have not tested with all possible output choices users have.
Keep us informed as to your tests. Thanks.