flatpak sandbox will lose downloads with certain XDG_DOWNLOAD_DIR
I have my XDG_DOWNLOAD_DIR set to /data/pony/Downloads (it's on an NFS mounted volume, I don't mount it under my $HOME, which is /home/pony), Fragments in flatpak will pick this as a default, but it seems it's not accessible within the sandbox, so the download goes to just some overlay (pardon me, not sure how flatpak does this) and it will never be accessible and is lost after I exit the Fragments later. This is completely silent, no error ever reported. I'm not sure if it's a Fragment flatpak issue or general flatpak issue, as you do allow xdg-download access in the manifest.
Running latest fedora 30, flatpak 1.4.2, Fragments from Flathub.