Andi, thank you for your answer.
The old Synchron Prime folder was renamed by Vienna Assistant, while the new one was being installed. I then deleted it from the content drive.
My OS is Mac Monterey 12.7.6 on an Intel Mac.
Synchron Player is v1.3.1674.
To enable Flow, I don't load a Precision preset. I click on the rainbow, touch the Strings section, and select, say, "Violoncellos (8 players)".
When the Flow UI appears, I choose any or the presets, play any note, and see the range appear.
By the way, the Pizzicato preset doesn't show the range.
No other operation. This happens both with Synchron Player used as standalone and as a Dorico plugin.
Here is a video:
Wrong range in Flow
Paolo