Apple Watch 6 auto detect workout not working

Dear Apple.

I have a new Apple Watch 6 and have over the past few days experienced issues with activity tracking. I have the watch set to auto detect “Start Workout Reminder” which I use for runs and walks. This reminder to start workout usually activates after I have covered about a mile but sometimes much less. 

Now it fails to do this and only kicks in after three or four miles, if at all. When I then press the button to start workout it only detects that I have covered a mile. Sometimes it fails to work altogether. 

I have double checked that the Start Workout Reminder setting is set to ‘on’ and location services are ‘on,’ both on my Apple Watch and iPhone. I have restarted both my iPhone and Apple Watch and tried unpairing both devices, but the erratic issue persists. The software on both devices are up to date.  Is there anything else I should try or does it sound like this Apple Watch is defective? 

The watch is only three months old and is under warranty. 

I hope you can help.

All the best,

Douglas