Further testing has revealed the issue to lie with a LibreOffice grammar extension called LanguageTool.
This is a known issue in LanguageTool and removing the extension resolved the issue. See this bug in the LangugeTool bug tracker: https://github.com /languagetool-org/languagetool/issues/1217?_pjax=%23js-repo-pjax- container -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1825513 Title: High CPU usage when large document open To manage notifications about this bug go to: https://bugs.launchpad.net/df-libreoffice/+bug/1825513/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs