[GSS]6.4.x SessionNotFoundException popup after completing task through business central

To reproduce the issue - used mortgage-demo from the jboss-brms-bpmsuite-6.4-quickstarts downloaded from Red Hat Customer Portal.

Here are the steps:

1. Follow the steps given in the README file in the jboss-brms-bpmsuite-6.4-quickstarts/jboss-bpmsuite-example folder to install application;
2. Navigate to "MortgageApplication" project;
3. For this MortgageApplication project click on "Open Project Editor" -> click on the "Project Settings" button on the right and select "Deployment Descriptor";
4. Choose "PER_PROCESS_INSTANCE" runtime strategy and save the change;
5. Deploy the kjar "com.redhat.bpms.examples:mortgage:1" in business central;
6. Create a container "com.redhat.bpms.examples:mortgage:1" (Deploy -> Execution Servers -> Add Container and make sure that "PER_PROCESS_INSTANCE" runtime strategy is selected in the second step);
7. Start newly created container;
8. Create payload.json as:
**********************************
{"application":{"com.redhat.bpms.examples.mortgage.Application":{
"applicant":

,
"property":

,
"downPayment":100000,
"amortization":30
}
}
}
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9. Execute the following command in order to start the process:

**********************************
curl -X POST -u 'bpmsAdmin:bpmsAdmin123!' -H 'Content-type: application/json' -d @payload.json 'http://localhost:8180/kie-server/services/rest/server/containers/com.redhat.bpms.examples:mortgage:1/processes/com.redhat.bpms.examples.mortgage.MortgageApplication/instances'
**********************************
10. Open the task "Appraisal" through business central
11. Complete the task inserting value "500001" for "Appraisal Value"
12. Process is properly finished but the pop up error: "Unexpected error occurred: org.kie.internal.runtime.manager.SessionNotFoundException:No session found for context xxx" is shown in the UI.