Are you stopping your AKS cluster? This will reduce your pod count to 0. Any data that is not on a persistent volume will be deleted when the pods are removed, so I would start by double checking what drive your persistent volume claim is mapped to, and also keep in mind that if you have 4 pods and 4 disks attached, and each pod is changing the disks in different ways, each disk will have their own changes.
I would also review the best practices and use cases for storage in AKS to make sure that you are using the correct type of storage. Typically an AKS cluster that needs to make permanent changes to a data set will use a remote database or use Azure Files to connect all of your pods to a single persistent file share.
Can you share your storage class and persistent volume claim configuration for the cluster?