Ever since 4.3.0 release i have seen a number of reports about issues with upgrades on Debian/Ubuntu based systems.
One of the most common issues seems to be related to permissions, as Openfire for some reason is not able to update config files although users report permissions are correct and hasn't changed.
Another often mentioned issue is with timezone ID in the database connection string. This can be related to Java update, though Debian version doesn't have Java bundled. Users have to update timezone ID to something else.