This repo demonstrates a bug with Svelte 4.1.1, Svelte Kit 1.22.3.
You can check the bug page.
To use it:
npm install -D
Then:
npm run dev
Go to the home page, click on Submit
You see error messages appearing, they should have a fading transition, but it is not working.
If you set the transition to global, you can see how it slows down navigation by clicking on the other page link after the messages appeared.