Gatway issue

There were a couple of dashboards are running on scheduled basis. All of sudden, they are throwing an issue and failing. Here is the error description. What is the cause of failing the reports? Any suggestions

An error occurred while processing the data in the dataset.
Refresh failed:

Total Casualty Dashboard has failed to refresh.
Failure details: The last refresh attempt failed because of an internal service error. This is usually a transient issue. If you try again later and still see this message, contact support.
{"error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","pbi.error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","parameters":{},"details":[{"code":"DM_ErrorDetailNameCode_UnderlyingErrorCode","detail":{"type":1,"value":"-2147467259"}},{"code":"DM_ErrorDetailNameCode_UnderlyingErrorMessage","detail":{"type":1,"value":"Oracle: ORA-03135: connection lost contact\nProcess ID: 60327\nSession ID: 599 Serial number: 6941\n"}},{"code":"DM_ErrorDetailNameCode_UnderlyingHResult","detail":{"type":1,"value":"-2147467259"}},{"code":"Microsoft.Data.Mashup.ValueError.DataSourceKind","detail":{"type":1,"value":"Oracle"}},{"code":"Microsoft.Data.Mashup.ValueError.DataSourcePath","detail":{"type":1,"value":"dw"}},{"code":"Microsoft.Data.Mashup.ValueError.ErrorCode","detail":{"type":1,"value":"-2146232008"}},{"code":"Microsoft.Data.Mashup.ValueError.Message","detail":{"type":1,"value":"ORA-03135: connection lost contact\nProcess ID: 60327\nSession ID: 599 Serial number: 6941\n"}},{"code":"Microsoft.Data.Mashup.ValueError.Reason","detail":{"type":1,"value":"DataSource.Error"}}],"exceptionCulprit":1}}} Table: Parent Reporting Unit.
Next refresh for Total Casualty Dashboard is scheduled for July 2, 2020 14:00 UTC.

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Technical Information

Activity Id:
c5d99572-ba8b-477b-acb1-53c137fa9d83

Request Id:
9dc1cee0-1bfa-4c3e-8982-f9d1af852ff3

Cluster Name:
WABI-US-NORTH-CENTRAL-redirect.analysis.windows.net

Refresh Start Time:
July 1, 2020 14:02 UTC

Refresh End Time:
July 1, 2020 14:20 UTC