It appears that the management_api access token do not renew during normal operations and requires a restart of the splunk instance to force a renewal. These tokens are short-lived (59 min 59 sec). After which no ms:o365:management sourcetype data are successfully retrieved. Waited several hours before restarting. No data was retrieved until a restart was performed which resumed the data ingestion for this sourcetype.
Has anyone observed this behavior and resolved this successfully?
You can check the status of your certificate by going to O365 Troubleshooting tab in the add-on. You should see the text "Auto-generated and verified as valid" or similar depending on whether you used generated certificate or your own certificate.