Why don't you want to update to the latest version? There's no advantage to being on 11.7 or 11.6. I don't know why it happened, sysupdater hasn't been recommended for years, so I am not sure what sorts of things can go wrong with it.
To fix your actual problem, if it isn't caused by being on an old Luma, and you don't want to restore a backup (or you don't have one), try doing a CTR transfer
https://www.3ds.guide/ctrtransfer