Is it a chroot issue? Interestingly, OpenBSD services seem to be moving away from chroot now that it has unveil. (Not that that would help you here and now.)
Yes. In my particular case I was setting up a server for some non-technical users to share files with me via FileZilla. So I use ChrootDirectory %h to restrict users to their home directory. Even if it wouldn't be a security issue to omit this, my users would be confused by seeing the whole /usr, /bin, /var etc. directory hierarchy show up in FileZilla. And even if they could learn their way around it, I don't want them to see the whole directory hierarchy. I just want them to see their own files.
Granted, this could be solved by symlinks if SFTP provided a way other than chroot to change the user-perceived home directory. But the fact that mount --bind works across filesystem namespace changes makes it more robust and useful in my book.
https://unix.stackexchange.com/questions/198590/what-is-a-bi...
There is something here that might solve your problem: nullfs. Check the stack exchange link.
I don't use bsd, so this is just me sharing what I found out.