So something wrong here.

If it were my device and I knew what I did I'd just set ssu to correct version and do the system upgrade.
But reading all those messages on forum.sailfishos.org I suggest:
install sfos-upgrade from olf found on openrepos.net
make sure you have lots of space on rootfs
do the btrfs balancing
backup your precious data
run sfos-upgrade from cli like
devel-su
sfos-upgrade 3.4.0.24