Yes, see “[Bug] /usr/libexec/sailfish-osupdateservice osupdate-check sets ssu re”.
How come that the new telephone-dialog is shown?
You do have (at least parts of) SFOS 3.4.0 installed.
Can I force a reinstall of 3.4 although the phone thinks it has 3.4 on it?
That is what " sfos-upgrade --verify " is for: Just read its documentation.