I've had my VA3M for about 2 weeks now and I've only encountered an issue like this once. Try powering the watch off then turn it back on and see if that helps. My issue was the watch seemed to be partially frozen at night when I wasn't wearing it and said I had burned over 1000 calories. I turned it off and then back on and it has been fine since. Apologies if you've already tired this and it hasn't helped
Eikalipse I think Garmin gives over estimates for walking - did your dog walk create an activity with calories attached that you can see? I have a tracked 3K walk that was a gentle stroll and its given me 650 calories and yet I have a 10K easy run that's only given me 730 calories (that is with a Fenix 5+ but I assume the algorithms are same/similar)