After a long struggle of not understanding what the problem was, one query from our community helped me fix the problem.
For documentation purposes;
When I connected the data (blue) line from the proxy to the properties I was using of the proxy, it was not just unproductive but in-turn counter productive. From the Outlook's FindEmail method, I extract proxy for mail, and then MUST NOT connect the data line to email's subject/body through the flow. And that's where I got my email body/subject of the mail I was referring to without being deleted after reading it.
I'm not sure if this was the solution that fixed it, but when I tried this, I no longer have deleted subject/body from the specific email that I'm reading from Outlook.