Hi, we constantly improve LanguageTool. We have 2 million installations of our add-on across browsers, and so far, nobody else complained about the add-on becoming slower. I suspect this might be an issue specific to your system. Feel free to contact our support. You can find the email at https://languagetool.org/legal.

Update: Neither we nor any other user can confirm the issue, so please contact our support with more details about your browser version, operating system and other add-ons in use.