@vfdev-5 I am a bit confused. I use the same evaluator for both train_loader and val_loader. Are the metrics calculated during training, or does the evaluator iterate the set again after the training epoch (with other random transforms) , just without updating the weights?
On the train set, the metrics should take into account the samples of the whole epoch (512 samples) and not just the len(train_loader). Having batch_size=1,  I should have 512 CE losses and calculate the mean. And IoU should be averaged for 512 samples (not 172).