I confirm, this still exists in Debian 10 (Buster). Debian Desktop GNOME3...xRDP package seems to be missing PolicyKit configuration files for GNOME3 shell.
I also wish to add that org.freedesktop.packagekit.system-sources-refresh should be added to this list. There are also other PolicyKit configurations related to using GNOME Control Center.
Additionally, GNOME Keyring isn't getting unlocked with PAM.
sudo bash -c "cat > /etc/pam.d/xrdp-sesman" <<EOF
#%PAM-1.0
@include common-auth
auth optional pam_gnome_keyring.so
@include common-account
@include common-session
session optional pam_gnome_keyring.so auto_start
@include common-password
EOF