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Stateful service runs on multiple replicas (by default 3 partitions) to take care of data failures.
As you are running a single node cluster you are seeing issues. To avoid data loss, it is recommended to run stateful service on more nodes.
Please check this FAQ document for mode information.
In ApplicationManifest.xml you can set the Replica count Default value to 1 (by default it is 3, but this is not recommended for stateful service).