Unfortunately, I can't help much, I spent 3~4 hours on debug and no luck, it require more time on debug, but I think it should done by `terser` contributors, feel free to report in `terser` repo and provide information about `compress.unused: false` is fix the problem. Nothing to fix on our side, sorry, I helped as much as I could

My **BIG** recommendation is drop IE 11, I know that some clients still require it, but it's time to tell them no, it is not possible do good and it is very slow.

As workaround you can setup `terser-webpack-plugin` manually using `vue.config.js` and setup `compress.unused: false`.

Feel free to feedback