Not sure if this help, but I think its significant - the model’s outputs for the test set are very very close to each other.
0.33960407972335815, 0.311821848154068, 0.34857410192489624

The average standard deviation for the whole test set between predictions for each image are (softmax):
0.017695341517654846

I have also created a confusion matrix for the test set below:
confusion (1)1800×1200 67.6 KB
Can anyone help me?
Edit: On the training set, the average std for the outputs is 0.2261 @tom