Metronome

Just tried to replicate this (using the metronome for the very first time). Gesture backlight worked fine.

One thing that is not mentioned in your post is the Backlight settings During Activity (from the system menu),

Thanks for the response and for trying to replicate the issue.  Backlight settings are default (8 seconds).  I've just tested again -same problem is still occurring.  I also tested starting a run (no metronome, backlight works) turning on metronome with activity still going - back light on wrist turn stops working, turn metronome off again with activity still running - backlight on wrist turn works again.

Just tried the mid-run metronome activation as you describe, and that seemed to work OK. About the only thing I noticed was that having the metronome set to Vibrate seemed to decrease the sensitivity of gesture detection. A definite "flick" of the wrist would activate the backlight, but a slow and gradual turn of the wrist may not. I couldn't observe any change in gesture detection when the metronome was set to Sound only. I am assuming that the movement of the watch from the vibration motor interferes with the ability of the accelerometers to pick up a slow wrist turn?

Although I've got to say that having the metronome vibration on for any length of time  would have me ripping the watch off in annoyance and throwing it away. Given I normally run along a riverside trail, that could be disastrous for my watch... 

Heya, thanks for digging further.  I carried out the same test - vibrate is what's causing the problem.  No matter how vigorously I turn my wrist, backlight will not work with metronome set to vibrate.  Metronome set to 'tone' the wrist gesture activates backlight perfectly well.  The tone is impossible to hear with headphones on - so no metronome for my runs.  Weird that yours works differently.  Thanks again.