Do we ever explain/explore why the chinstraps are not present in the the predictions in the confusion matrix? is it the specific random seed? the train/test has stratify/shuffle=True so the right steps were taken to avoid this issue... (short of a bad seed)
It might be worth answering so that learners can see how to tackle the "black box" nature of DL/NNs. Leaving it unanswered or saying "a bad model" doesn't seem very satisfying or good practice.