Fenix 8 - 47 mm AMOLED crashing and turning off

I’ve seen similar posts recently, but I think my issue may be slightly different to others.

I believe this started after upgrading to 13.31, but I’m not 100% sure.

My watch started randomly turning off. Like, during or not during an activity. It’s not re-booting, it’s turning off. 

It seems to happen every time I’m in a running activity. I can power it back on and it comes back to the screen where I can resume. 

I’ve reset to factory settings, I’ve downgraded to 12.35 - it does still power off on 12.35. 

After three support calls and one chat, I’ve upgraded to 13.31 again and submitted logs.

But, it’s unusable now for a running watch so I’ve resorted to my trusted Forerunner 945. 

The reason I’m posting is, could this be a faulty Fenix (hardware fault) rather than a software issue? Should I push Garmin support for a replacement?

Thanks.