While training semantic segmentation  i had 23 classes including Ignore label, during my prediction i get only 22 classes. I have used cross entropy loss and provided ignore index as 255.
What looks from the predicted image is one of the class (class_name:vegetation, id:21)  merge with ignore index as seen in the below image.
Below image shows the Unique values for Ground truth and Prediction along with Original, GT  & Predicted image.
Please help with what may have caused this!!!

Screenshot from 2020-01-10 18-08-211154×336 115 KB