Today i have checked Mail Flow dashboard in Security & Compliance and it showed there is a domain loop somewhere. When i have pressed on details, it showed there are 12 messages and i have clicked to see sample messages. It returned No data available. I have filed a case and support specialist told me he is not seeing such feature on their tenant and this is probably some not fully developed feature. I'm not sure if i should believe this. I guess, as S&C looks half baked most of the time anyway..
The Mail Flow insights are a fairly recent addition and they might be still in development, but that's no excuse for the **bleep**ty reply you got from the support agent. In case you haven't tried it already, you can use the Feedback button on the SCC to query about this.
Actually, later i have received an email from support if i am satisfied and i told that im not and i find such SC quality unacceptable. So they have escalated it and contacted me again. Gathered logs with some special tool (i think it combines psr, feedly and office troubleshooter). Also asked for message traces for 2 months. Sent them traces today.
I have tried to use feedback option in admin center many times, but only once or twice got a reply.