Understanding outputs from ANN and how to improve validation loss
500K is decent data size. So, we can have a larger test set and also the network should be bigger.
Try the below listed suggestions -

Have a bigger model e.g. 200 Neurons, 5-6 layers
The test set should be 25%-30% since you have a decent dataset size
Keep LR to default
Increase batch size a bit as it's still fluctuating
Data should be standardized
Try adding Regularization when it starts overfitting