the resolution, incase anyone is interested, was to duplicate a Model Source, re-add the test data and retrained.

Feedback assistant report, just sent.

The number that appears below the description of the issue in the feedback assistant app is FB17236811 So hope this is what your are looking for.

Is it possible to say if this has been found to be a bug? and if so when might a fix be delivered?

WireShark logs have been uploaded for both iPad and iPhone, for the case FB17236811 In the case of the former a DORA cycle runs to completion. In the of the iPhone there is a corresponding "Offer", from the RN171, for each iPhone "Discovery" however it is not matched with a "Request". Either the iPhone doesn't see or silently rejects the "Offer". Interesting!

I have raised a Feedback Assistant on this issue FB18703147

How should I interpret the lack of response, from Apple, regarding this issue? I guess I'll have to push it to a "Code-level support request" any wisdom from other forum residents?

this did the trick: https://stackoverflow.com/questions/79253685/ios-phasset-to-check-if-a-video-is-hevc-or-h-264