Offline dictation not available after software updates on iPhone and iPad

I have noticed that after each software update (the last, to iOS 17.4.1.) the offline dictation is not more available, but only the online dictation without the new functionality that allows the user to tipe on the virtual keyboard and dictate at the same time. With the preview updates the offline dictation returned after some time, I hope that also this time the problem will be resolve soon, but I want to know the causes of this problem. Thank you