The operator manages the scale and configuration file to provide to Kubernetes.

If changes are made in the hydrolixcluster.yaml with something not recognized by Kubernetes, the operator will not deploy your changes and will rollback to the previous version.

In order to understand what failed in the update it is important to look at the logs of the operator pod:

kubectl logs -l app=operator

The operator can change the scale of any of the stateless deployment, it also creates and manages statefulset.
But the operator can't change the PVC of a statefulset, so if you want to resize or modify the disk of a statefulset, you need to manage this change outside of the operator.

If you have pods that are not getting deployed it might be due to lack of ressources in your K8 cluster.
You can use the describe command from K8 to get more details on what ressources is missing in your cluster:

kubectl describe pod $podname