I encountered this problem with deja-dup-18.0. I could deal with it by disabling in gnome-session the GPG service of the gnome-keyring-daemon, but without completely killing the gnome-keyring-daemon. In my case that service is started by a command like: gnome-keyring-daemon --start --components=gpg. It seems that duplicity is not compatible with the gpg-agent from gnome-keyring-daemon but I couldn't find any confirmation on this.
I encountered this problem with deja-dup-18.0. I could deal with it by disabling in gnome-session the GPG service of the gnome-keyring- daemon, but without completely killing the gnome-keyring- daemon. In my case that service is started by a command like: gnome-keyring- daemon --start --components=gpg. It seems that duplicity is not compatible with the gpg-agent from gnome-keyring- daemon but I couldn't find any confirmation on this.