@Aatos Media, this is probably by design. TestFlight versions are assumed to behave as “Live” versions, not test versions. When you test on device via installing locally, you get the dialog every time. But when the app is live, Apple controls how often the dialog shows and it won’t show every time. Think of it as requesting it to show the next time it’s eligible to show.
Part of Apple requiring this is they want to control the display so that developers don’t ask too often.
Rob