I have now tried 3 rides broadcasting my HR to my Edge 1000 whilst recording the activity on my 5 plus. Each time the bradcat stops after about a minute. If I just broadcast the HR it all works fine.
Interesting. My Fenix 5 (not plus) used to always stop after about a minute in broadcast mode, even when not recording an activity. The 9.20 update last week seems to have finally fixed that problem. Will be a pity if it isn’t fixed while recording.