Error on calories report on App Connect

Hello, 

I'm using my montana 700 with E-MTB and I've set a data field to shown a burned calories  during the activity.

When I look at the report on the "connect" app, the calories shown are different from those shown in the data field, even though they belong to the same activity .
Also it seems that the ones shown in the "connect" app are underestimated
Does anyone have the same problem?
How can I solve it?