Dehydrated means the service instance is waiting on some event and has been removed from memory – state is maintained within the database.
This service instance will be rehydrated when an event, it is waiting on, occurs.
This is a mechanism to free resources on the server. Some service instances can last hours, days or even months. Rather than maintain all service instances within memory, they are dehydrated after a period of no activity.
If your service instance has been dehydrated, you need to determine what it is waiting on.
Have you checked the event log for error messages