I got the LB score of 0.901 by simply using SnapMix augmentation and model ensemble.
Detailed results can be found as below.
Single model result (single fold, no tta, no extra training data)
Resnet50 : LB 0.891 Notebook for training
Model ensemble ( no tta, no extra training data):
Resnet50 (5 folds) : LB 0.897
Resnet50 (5 folds) + Resnet101(5 folds): LB 0.899
Resnet50 (5 folds) + Resnet101(5 folds) + ResNext101(5 folds): LB 0.901
How I got LB 0.901 in a simple way.