Thanks, @Manuel_Alejandro_Dia for your reply!
Let me rephrase the questions:

Is it a general rule that the class weights should be pre-calculated for the entire training data rather than calculating for each batch on the fly?
Is the use of “class weights” in loss calculation and “data augmentation” mutually exclusive?
Should one use weights calculated from each input batch of A) augmented images or B) images before augmenting them?