See this issue which was closed due to no repro.
The problem is that there is decoupling between the scoped CSS id's and the data-v-xxxx ids that Vue generates when using vite's build --watch (or watch: true in the config).
Use: npx degit https://github.com/earlAchromatic/Vite-Watch-Scoped-CSS.git pnpm i, pnpm build and then pnpm play to build and start servers.
Then change the component template in component.vue you will see that the styles are no longer being applied properly.