After a few weeks of setting up ServiceNow, the configuration is reverted to default

This issue is caused by the Data Retention Policy being applied to the objects that contain the ServiceNow configuration: ServiceNowIntegrationConfig and SNIntegrationConfigForOneService.
This was identified as defect FOG-8622
WORKAROUND
Set a custom Auto-delete policy for ServiceNowIntegrationConfig and SNIntegrationConfigForOneService objects to be kept indefinitely in the Object Cleanup dashboard.
ServiceNowIntegrationConfigSNIntegrationConfigForOneService
Note: Object Cleanup dashboard has two modes which are toggled by a link in the lower-right corner, the example screenshot above is the Object Management view.
>STATUS
Waiting for fix in a future release of Foglight.