So I have found the issue
I have mounted my dropbox to /mnt/addons/dropbox
This works fine. I can see the files there.
However, when I copy the files to /mnt/user/dropbox it seems to write to rootfs for some reason. I used to do this before without any issues. I don't know where on rootfs it is writing nor why.
How should I correctly mount my dropbox so that I can copy it to a /mnt/user/ share?