Comment 6 for bug 1694455

Staying on gnome-control-center bluetooth pane while receiving file works too.
When so dbus session show it registers itself to obexd RegisterAgent with '/org/gnome/share/agent'.
As soon as we exit the gnome-control-center bluetooth pane it unregister itself and stop advertising itself as org.bluez.obex.Agent1 on the dbus session bus.
obexd thus fails as no agent is available.

part 2 is https://bugs.launchpad.net/ubuntu/+source/gnome-bluetooth/+bug/1645631 though me might want to keep it there as there are 4 different issues in this previous report. My test shown that when I was with an agent the file goes temporarily to $HOME/.cache/obexd/<random name> then to the Downloads folder. So I do not confirm the bug reports 1645631 findings.
This refutes the root folder is not correct issue (dbus monitor shows the same cache dir with or without an agent).

gnome-file-share-properties is still available in gnome-user-share on ubuntu. As you shown it registers itself and stays available to the obex server obexd. So it is a correct workaround. But it might go away like it did in debian. A fix upstream is more than wanted. Mostly an agent that runs session wide not gnome-control-center a bluetooth pane that is never active except when pairing.