Fenix 5 Rebooting - hardware or software?

Hi, my Fenix 5 (APAC) has started spontaneously rebooting. It started happening a couple of weeks ago.

Firmware is v14.20 (APAC latest), and looking back at my previous activities this was updated from 14.10 on either October 3rd or October 4th and from 13.30 on September 17th.

It happens most during a workout (5-6 times in a 10k run last week) but also happens occasionally through the day when I'm not actively using the watch. It seems to be movement related and I can also sometimes make it happen by giving my wrist a quick flick like the backlight gesture, which makes me suspect it's hardware.

I've done a factory reset and set it up again without installing any watch faces, data fields or other CIQ apps and it's still happening.

I've had a look at the files in GARMIN\EVNTLOGS and GARMIN\DEBUG but they don't seem to correlate with any times I've experienced a reboot.

Anything else I can do to confirm this is a hardware issue? I've ordered a Fenix 6 Pro anyway but I'd quite like to sell my Fenix 5, but it might have to go on eBay as spares/repairs :/

Cheers,