Vault Sealed error

The Vault version is 1.7.0. We are using a systemd file to create a vault docker application. We took backup of Master Key and Tokens. During restart of docker service (cmd sudo service docker restart ) our vault application also got restarted. But when we try to access the vault, it is in sealed state and the master key and tokens are not working. Can someone suggest me how do I solve this issue? We are unable to use our Kubernetes Blockchain applications which are in production. Our vault application is deployed in a separate VM.