Just FYI: You can re-install Ubuntu and flavors (ie. Lubuntu) without losing any data files, and it would be my first option if you had to re-install (in fact I think of it as my fallback if I have problems, or just don’t have the time to release-upgrade as it’s so fast).
In Lubuntu’s QA Testing Checklist I’m referring to the Install using existing partition and it’s what I’d perform if you felt you needed to re-install. Without the format (and re-use of existing partitions) user files aren’t touched, plus your manually installed packages are noted, and re-installed if available for the new release. If you have problems with that, the clean install (ie. with format) option is still available.