Lost nearly 5000 Ostron standing, How?

As the title says I was 10 away from what I needed to rank up, so I did a shrine defense to just get it quickly. After the mission I was 5000 lower than what I was when I went in. Is this a bug? Does Shrine defence cost standing to enter? Any ideas on what could have happened?

Its not a big deal, just wonder how it could have happened so I can try and avoid it in the future