My only idea is that you maybe didn’t leave LibreOffice after the installation of libreoffice-java-common? (including the quick starter, if that still exists, not sure)
I’ve never seen the Quick Launcher in Kubuntu, so I don’t know where it is, if it exists. But in any case, I did leave LibreOffice, and then, for good measure, rebooted the whole computer. I also checked that the Libre-Office reference to java was correct.
I did have a previous version of Language Tools installed. Could that have any effect? I assume it was overwritten.
I can’t see anything further to do. Maybe when the new Kubuntu distribution comes out next month it will work?