When I woke my Pop!_OS 20.04 laptop this morning (already logged in), Deja Dup started automatically as usual, but failed with message similar to issue #77 and #50 (closed) (both closed). I do not recall if the last flatpak update was yesterday or the day before so I am not sure if that is relevant. I restarted and then everything proceeded as normal. Perhaps the latest flatpak update requires a restart, at least in some systems?