Holes in segmentation for OBIA method

Hey !

I try to use Object Based Image Analysis method to classify an image in 2 classes. I followed the following process : Segmentation -> ZonalStatistics -> TrainVectorClassifier -> VectorClassifier.

I have 2 problems :
-after segmentation, when zooming, I noticed there are holes in the segmentation (below). I don’t understand the reason why there are those holes (under the segmentation shapefile, this is my photo). Can someone explain it to me ?
-after all the process, I got a shapefile layer, with my two classes, but the classification is not good at all. Maybe there are not enough samples of each class in the shapefile I created at the beginning for classification ? Are there other possible reasons to explain it ?

Thank you for your help

Can you provide the command lines? Can you identify which application is responsible?
It looks like these holes came from an over simplification of the original segmentation.