I am encountering numerous flatpak problems.
1 ) Many flatpaks will not install. I get a variety of errors. The flatpak downloads but then near the finish gets an error "Connection reset by peer"
2 ) Flatpaks that do install will only run in terminal. And while they are running I get numerous dbus warnings.
3 ) Flatpaks that do manage to make it on the menu list will not launch from the menu
4 ) Some flatpaks will not update. Error "connection to peer reset"
5 ) Error message "Can't find temporary directory"
I did not have any of these problems in SparkyLinux ( which uses Debian 9.4 )