Negative Calorie Adjustment

I wear my Garmin Fenix 6 most of the day and have it sync to MFP to track calorie burn.

From 6-8pm, I take it off to train martial art.

I wear a Polar Verity Sense to track my calorie burn which also syncs to MFP.

I find that by the end of the day, MFP keeps giving me a negative calorie adjustment off my Garmin even though I am active the rest of the day when I wear it - and it registers a positive figure throughout the day.

It only goes to negative after I finish training.

Should I just leave it off?