This happens connecting a host allowing password authentication:
=======
Oct 13 19:36:28 my_machine gvfsd[758]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s permissive.remote.host sftp
Oct 13 19:36:28 my_machine gvfsd[758]: ### SFTP: handle_login #1, initial_connection = 1 - user: me, host: permissive.remote.host, port: -1
Oct 13 19:36:34 my_machine gvfsd[758]: ### SFTP: handle_login #1 - prompt: "me@permissive.remote.host's password: "
Oct 13 19:36:34 my_machine gvfsd[758]: ### SFTP: handle_login #1 - asking for password...
Oct 13 19:36:51 my_machine gvfsd[758]: ### SFTP: handle_login #1 - prompt: ""
Oct 13 19:36:53 my_machine gvfsd[758]: ### SFTP: handle_login #1 - password_save: 0
Oct 13 19:36:53 my_machine gvfsd[758]: ### SFTP: handle_login #1 - ret_val: 1
Oct 13 19:36:53 my_machine gvfsd[758]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s permissive.remote.host sftp
Oct 13 19:36:53 my_machine gvfsd[758]: ### SFTP: handle_login #2, initial_connection = 0 - user: me, host: permissive.remote.host, port: -1
Oct 13 19:36:59 my_machine gvfsd[758]: ### SFTP: handle_login #2 - prompt: "me@permissive.remote.host's password: "
Oct 13 19:36:59 my_machine gvfsd[758]: ### SFTP: handle_login #2 - using credentials from previous login attempt...
Oct 13 19:36:59 my_machine gvfsd[758]: ### SFTP: handle_login #2 - prompt: ""
Oct 13 19:36:59 my_machine gvfsd[758]: ### SFTP: handle_login #2 - ret_val: 1
========

While trying to connect a host with exclusvive ssh-key access, journalctl tells:
========
Oct 13 19:36:08 my_machine gvfsd[758]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s strict.remote.host sftp
Oct 13 19:36:08 my_machine gvfsd[758]: ### SFTP: handle_login #1, initial_connection = 1 - user: me, host: strict.remote.host, port: -1
Oct 13 19:36:09 my_machine gvfsd[758]: ### SFTP: handle_login #1 - password_save: 0
Oct 13 19:36:09 my_machine gvfsd[758]: ### SFTP: handle_login #1 - ret_val: 1
Oct 13 19:36:09 my_machine gvfsd[758]: ### SFTP: stderr: Permission denied (publickey).
Oct 13 19:36:09 my_machine gvfsd[758]: ** (gvfsd:758): WARNING **: dbus_mount_reply: Error from org.gtk.vfs.Mountable.mount(): Zugriff verweigert
=======

new one - failing (access denied):
================
Oct 30 00:22:22 my_machine gvfsd[1047]: ** (process:1315): WARNING **: Failed to setup SSH evironment: The name org.gnome.keyring was not provided by any .service files (g-dbus-error-quark, 2)
Oct 30 00:22:22 my_machine gvfsd[1047]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s remote.host sftp
Oct 30 00:22:22 my_machine gvfsd[1047]: ### SFTP: handle_login #1, initial_connection = 1 - user: me, host: remote.host, port: -1
Oct 30 00:22:22 my_machine gvfsd[1047]: ### SFTP: handle_login #1 - password_save: 0
Oct 30 00:22:22 my_machine gvfsd[1047]: ### SFTP: handle_login #1 - ret_val: 1
Oct 30 00:22:22 my_machine gvfsd[1047]: ### SFTP: stderr: Permission denied (publickey).
Oct 30 00:22:22 my_machine gvfsd[1047]: ** (gvfsd:1047): WARNING **: dbus_mount_reply: Error from org.gtk.vfs.Mountable.mount(): Zugriff verweigert
================

Restarting dbus as root yields:
=========
[root@myhost ~]# systemctl restart dbus
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.
=========

Journalctl output after Xfce-Login (root restarted dbus) - success:
==================
Okt 29 23:56:24 my_machine org.gtk.vfs.Daemon[1703]: ** (process:1911): WARNING **: Failed to setup SSH evironment: The name org.gnome.keyring was not provided by any .service files (g-dbus-error-quark, 2)
Okt 29 23:56:24 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s permissive.remote.host sftp
Okt 29 23:56:24 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: handle_login #1, initial_connection = 1 - user: me, host: permissive.remote.host, port: -1
Okt 29 23:56:26 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: handle_login #1 - password_save: 0
Okt 29 23:56:26 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: handle_login #1 - ret_val: 1
Okt 29 23:56:26 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: spawn_ssh: ssh -oForwardX11 no -oForwardAgent no -oPermitLocalCommand no -oClearAllForwardings yes -oProtocol 2 -oNoHostAuthenticationForLocalhost yes -l me -s permissive.remote.host sftp
Okt 29 23:56:26 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: handle_login #2, initial_connection = 0 - user: me, host: permissive.remote.host, port: -1
Okt 29 23:56:27 my_machine org.gtk.vfs.Daemon[1703]: ### SFTP: handle_login #2 - ret_val: 1
==================