The reason you may see zero or negative calorie adjustments for your Withings App activity in MyFitnessPal is due to a difference in how MyFitnessPal estimates calories. Withings App estimates calories as you go, adjusting based on your current activity levels. MyFitnessPal must estimate calories for the rest of the day based on the data that has synced up to a certain time of the day.
Since the calorie projection above for Withings App is lower than the calorie estimates from MyFitnessPal, no calorie adjustments need to be made (with negative calorie adjustments disabled in MyFitnessPal).
However, if your Withings App calorie projection is greater than the calorie estimate from MyFitnessPal, they would show as a positive adjustment as seen below.
More information about calorie adjustments made in MyFitnessPal can be found here.