High AUC for training and validation , but very low AUC for TESTING set

Hello , i am currently running a resnet18 from scratch for a binary classification problem. The problem i am currently facing is while having a very good AUC score for both my training and validation data ( around 0.99 ) and also a low loss who decrease through the epoch .

When i am running my trained model on the testing data , i got a very low AUC score of 0.51 , meaning that my model don't predict anything …

auc binary classification data deeplearning good loss low running set testing training validation